USB flash drive,HDD and SSD 3
Latency[edit source | editbeta]
Latency is the delay for the rotation of the disk to bring the required disk sector under the read-write mechanism. It depends on rotational speed of a disk, Sony VGP-BPL14/B Battery
Sony VGP-BPL14B Battery measured in revolutions per minute (rpm). Average rotational latency is shown in the table below, based on the statistical relation that the average latency in milliseconds for such a drive is one-half the rotational period. Sony VGP-BPS12 Battery
Rotational speed
As of 2010, a typical 7,200-rpm desktop HDD has a sustained "disk-to-buffer" data transfer rate up to 1,030 Mbits/sec.[88] This rate depends on the track location; the rate is higher for data on the outer tracks (where there are more data sectors per rotation) and lower toward the inner tracks (where there are fewer data sectors per rotation); Sony VGP-BPS12/Q Battery
Sony VGP-BPS21A/B Batteryand is generally somewhat higher for 10,000-rpm drives. A current widely used standard for the "buffer-to-computer" interface is 3.0 Gbit/s SATA, which can send about 300 megabyte/s (10-bit encoding) from the buffer to the computer, and thus is still comfortably ahead of today's disk-to-buffer transfer rates. Sony VGP-BPS13 Battery
Sony VGP-BPS21/S Battery Data transfer rate (read/write) can be measured by writing a large file to disk using special file generator tools, then reading back the file. Transfer rate can be influenced by file system fragmentation and the layout of the files.[82] Sony VGP-BPS13A Battery
HDD data transfer rate depends upon the rotational speed of the platters and the data recording density. Because heat and vibration limit rotational speed, advancing density becomes the main method to improve sequential transfer rates. Sony VGP-BPS13A/B Battery
Sony VGP-BPS21A BatteryHigher speeds require more power absorbed by the electric engine, which hence warms up more. While areal density advances by increasing both the number of tracks across the disk and the number of sectors per track, Sony VGP-BPS13B/B Battery
Sony VGP-BPS21 Battery only the latter increases the data transfer rate for a given rpm. Since data transfer rate performance only tracks one of the two components of areal density, its performance improves at a lower rate.[citation needed] Sony VGP-BPS13/B Battery
Other considerations[edit source | editbeta]
Other performance considerations include power consumption, audible noise, and shock resistance.
Access and interfaces[edit source | editbeta]
Inner view of a 1998 Seagate HDD which used Parallel ATA interface
Main article: Hard disk drive interface
HDDs are accessed over one of a number of bus types, including as of 2011 parallel ATA (PATA, also called IDE or EIDE; described before the introduction of SATA as ATA), Sony VGP-BPS13B/Q Battery
Sony VGP-BPS15/B Battery Serial ATA (SATA), SCSI, Serial Attached SCSI (SAS), and Fibre Channel. Bridge circuitry is sometimes used to connect HDDs to buses with which they cannot communicate natively, such as IEEE 1394, USB and SCSI. Sony VGP-BPS13/Q Battery
Modern HDDs present a consistent interface to the rest of the computer, no matter what data encoding scheme is used internally. Typically a DSP in the electronics inside the HDD takes the raw analog voltages from the read head and uses PRML and Reed–Solomon error correction[89] to decode the sector boundaries and sector data, Sony VGP-BSP13/S Battery
Sony VGP-BPS15 Battery then sends that data out the standard interface. That DSP also watches the error rate detected by error detection and correction, and performs bad sector remapping, data collection for Self-Monitoring, Analysis, and Reporting Technology, and other internal tasks. Sony VGP-BPS14 Battery
Modern interfaces connect an HDD to a host bus interface adapter (today typically integrated into the "south bridge") with one data/control cable. Each drive also has an additional power cable, usually direct to the power supply unit. Sony VGP-BPS14/B Battery
Small Computer System Interface (SCSI), originally named SASI for Shugart Associates System Interface, was standard on servers, workstations, Commodore Amiga, Atari ST and Apple Macintosh computers through the mid-1990s, Sony PCG-6Z2M battery
by which time most models had been transitioned to IDE (and later, SATA) family disks. The range limitations of the data cable allows for external SCSI devices.
Integrated Drive Electronics (IDE), later standardized under the name AT Attachment (ATA, with the alias P-ATA or PATA (Parallel ATA) retroactively added upon introduction of SATA) moved the HDD controller from the interface card to the disk drive. Sony PCG-6X4M battery
Sony PCG-71316M battery This helped to standardize the host/contoller interface, reduce the programming complexity in the host device driver, and reduced system cost and complexity. The 40-pin IDE/ATA connection transfers 16 bits of data at a time on the data cable. The data cable was originally 40-conductor, Sony PCG-6X2M battery,
Sony PCG-71315M battery but later higher speed requirements for data transfer to and from the HDD led to an "ultra DMA" mode, known as UDMA. Progressively swifter versions of this standard ultimately added the requirement for an 80-conductor variant of the same cable, Sony PCG-4Q2M battery,
Sony PCG-91311M batterywhere half of the conductors provides grounding necessary for enhanced high-speed signal quality by reducing cross talk.
EIDE was an unofficial update (by Western Digital) to the original IDE standard, with the key improvement being the use of direct memory access (DMA) to transfer data between the disk and the computer without the involvement of the CPU, Sony PCG-4R1M battery
Sony PCG-91112M battery an improvement later adopted by the official ATA standards. By directly transferring data between memory and disk, DMA eliminates the need for the CPU to copy byte per byte, therefore allowing it to process other tasks while the data transfer occurs. Sony PCG-4Q1M battery
Fibre Channel (FC) is a successor to parallel SCSI interface on enterprise market. It is a serial protocol. In disk drives usually the Fibre Channel Arbitrated Loop (FC-AL) connection topology is used. FC has much broader usage than mere disk interfaces, and it is the cornerstone of storage area networks (SANs). Recently other protocols for this field, Sony PCG-71C11M battery
Sony PCG-71411M batterylike iSCSI and ATA over Ethernet have been developed as well. Confusingly, drives usually use copper twisted-pair cables for Fibre Channel, not fibre optics. The latter are traditionally reserved for larger devices, such as servers or disk array controllers. Sony PCG-71D14M battery
Serial Attached SCSI (SAS). The SAS is a new generation serial communication protocol for devices designed to allow for much higher speed data transfers and is compatible with SATA. SAS uses a mechanically identical data and power connector to standard 3.5-inch SATA1/SATA2 HDDs,
Sony PCG-61712M battery and many server-oriented SAS RAID controllers are also capable of addressing SATA HDDs. SAS uses serial communication instead of the parallel method found in traditional SCSI devices but still uses SCSI commands. Sony PCG-61511M battery
Serial ATA (SATA). The SATA data cable has one data pair for differential transmission of data to the device, and one pair for differential receiving from the device, just like EIA-422. That requires that data be transmitted serially. A similar differential signaling system is used in RS485, LocalTalk, USB, FireWire, and differential SCSI. Sony PCG-6Z2M battery,
Integrity and failure[edit source | editbeta]
Close-up HDD head resting on disk platter; its mirror reflection is visible on the platter surface
Main articles: Hard disk drive failure and Data recovery
Due to the extremely close spacing between the heads and the disk surface, HDDs are vulnerable to being damaged by a head crash—a failure of the disk in which the head scrapes across the platter surface, Sony PCG-6X2M battery,
Sony PCG-71318M battery often grinding away the thin magnetic film and causing data loss. Head crashes can be caused by electronic failure, a sudden power failure, physical shock, contamination of the drive's internal enclosure, wear and tear, corrosion, or poorly manufactured platters and heads. Sony PCG-4Q2M battery
The HDD's spindle system relies on air pressure inside the disk enclosure to support the heads at their proper flying height while the disk rotates. HDDs require a certain range of air pressures in order to operate properly. Sony PCG-4R1M battery
Sony PCG-71315M batteryThe connection to the external environment and pressure occurs through a small hole in the enclosure (about 0.5 mm in breadth), usually with a filter on the inside (the breather filter).[
Sony PCG-91311M battery90] If the air pressure is too low, then there is not enough lift for the flying head, so the head gets too close to the disk, and there is a risk of head crashes and data loss. Specially manufactured sealed and pressurized disks are needed for reliable high-altitude operation, above about 3,000 m (9,800 ft).[91Sony PCG-4Q1M battery
Sony PCG-91112M battery] Modern disks include temperature sensors and adjust their operation to the operating environment. Breather holes can be seen on all disk drives—they usually have a sticker next to them, warning the user not to cover the holes. Sony PCG-71C11M battery
Sony PCG-71511M batteryThe air inside the operating drive is constantly moving too, being swept in motion by friction with the spinning platters. This air passes through an internal recirculation (or "recirc") filter to remove any leftover contaminants from manufacture, Sony PCG-71D14M battery
Sony PCG-71411M batteryany particles or chemicals that may have somehow entered the enclosure, and any particles or outgassing generated internally in normal operation. Very high humidity for extended periods can corrode the heads and platters. Sony PCG-61511M battery
For giant magnetoresistive (GMR) heads in particular, a minor head crash from contamination (that does not remove the magnetic surface of the disk) still results in the head temporarily overheating, due to friction with the disk surface, Sony PCG-61611M battery
Sony PCG-61712M batteryand can render the data unreadable for a short period until the head temperature stabilizes (so called "thermal asperity", a problem which can partially be dealt with by proper electronic filtering of the read signal). Sony VPCSA2Z9E battery
When a mechanical hard disk requires repairs, the easiest method is to replace the circuit board using an identical hard disk, provided it is the circuit board that has malfunctioned. In the case of read-write head faults, they can be replaced using specialized tools in a dust-free environment. If the disk platters are undamaged, Sony SVS13AA11M battery
Sony PCG-4121GM battery they can be transferred into an identical enclosure and the data can be copied or cloned onto a new drive. In the event of disk-platter failures, disassembly and imaging of the disk platters may be required.[9Sony SVS131B12M battery
Sony PCG-41214M battery2] For logical damage to file systems, a variety of tools, including fsck on UNIX-like systems and CHKDSK on Windows, can be used for data recovery. Recovery from logical damage can require file carving. Sony SVS151A11M battery
Sony SVS151A12M battery
A 2011 summary of research into SSD and magnetic disk failure patterns by Tom's Hardware summarized research findings as follows:[93]
MTBF does not indicate reliability; the annualized failure rate is higher and usually more relevant.
Magnetic disks do not have a specific tendency to fail during early use, and temperature only has a minor effect; instead, failure rates steadily increase with age. Sony SVS1311E3EW battery
SMART warns of mechanical issues but not other issues affecting reliability, and is therefore not a reliable indicator of condition.
Failure rates of drives sold as "enterprise" and "consumer" are "very much similar", although customized for their different environments. Sony SVS1311P9EB battery
In drive arrays, one drive's failure significantly increases the short-term chance of a second drive failing.
3.0 TB 3.5" Seagate FreeAgent GoFlex plug and play external USB 3.0-compatible drive (left), 750 GB 3.5" Seagate Technology push-button external USB 2.0 drive (right), and a 500 GB 2.5" generic brand plug and play external USB 2.0 drive (front). Sony SVS1511L3ES battery
Sony SVS1511M3EW battery
External removable HDDs[note 11] typically connect via USB. Plug and play drive functionality offers system compatibility and features large storage options and portable design. External HDDs are available in 2.5" and 3.5" sizes, and as of March 2012 their capacities generally range from 160GB to 2TB. Common sizes are 160GB, 250GB, 320GB, 500GB, 640GB, 750GB, 1TB, and 2TB.[94][95] Sony SVS1511N3ES battery
External HDDs are available as preassembled integrated products or may be assembled by combining an external enclosure (with USB or other interface) with a separately purchased drive.
Features such as biometric security or multiple interfaces are available at a higher cost.[96] Sony SVS1511T9ES battery
External hard drives generally have a slower transfer rate than that of an internally mounted hard drive connecting through SATA.
Market segments[edit source | editbeta]
Desktop HDDs typically store between 60 GB and 4 TB and rotate at 5,400 to 10,000 rpm, and have a media transfer rate of 0.5 Gbit/s or higher (1 GB = 109 bytes; 1 Gbit/s = 109 bit/s). As of September 2011, the highest capacity consumer HDDs store 4 TB.[54] Sony SVS1511V9EB battery
Mobile HDDs or laptop HDDs, smaller than their desktop and enterprise counterparts, tend to be slower and have lower capacity. Mobile HDDs spin at 4,200 rpm, 5,200 rpm, 5,400 rpm, or 7,200 rpm, with 5,400 rpm being typical. 7,200 rpm drives tend to be more expensive and have smaller capacities,
Sony PCG-4121DM batterywhile 4,200 rpm models usually have very high storage capacities. Because of smaller platter(s), mobile HDDs generally have lower capacity than their greater desktop counterparts.
Sony VPCSE2V9E battery
Enterprise HDDs are typically used with multiple-user computers running enterprise software. Examples are: transaction processing databases, internet infrastructure (email, webserver, e-commerce), scientific computing software, and nearline storage management software. Enterprise drives commonly operate continuously ("24/7")Sony SVS1511V9ES battery
Sony VPCSE2F1E battery in demanding environments while delivering the highest possible performance without sacrificing reliability. Maximum capacity is not the primary goal, and as a result the drives are often offered in capacities that are relatively low in relation to their cost.[97] The fastest enterprise HDDs spin at 10,000 or 15,000 rpm, and can achieve sequential media transfer speeds above 1.6 Gbit/s[9Sony SVS1511W9EB battery
8] and a sustained transfer rate up to 1 Gbit/s.[98] Drives running at 10,000 or 15,000 rpm use smaller platters to mitigate increased power requirements (as they have less air drag) and therefore generally have lower capacity than the highest capacity desktop drives. Sony VPCSA3Q9E battery
Sony VPCSB4S9E battery Enterprise HDDs are commonly connected through Serial Attached SCSI (SAS) or Fibre Channel (FC). Some support multiple ports, so they can be connected to a redundant host bus adapter. They can be reformatted with sector sizes larger than 512 bytes (often 520, 524, Sony VPCCA3 battery
Sony SVE1511J1EW battery
528 or 536 bytes). The additional storage can be used by hardware RAID cards or to store a Data Integrity Field.
Consumer electronics HDDs include drives embedded into digital video recorders and automotive vehicles. The former are configured to provide a guaranteed streaming capacity, even in the face of read and write errors, while the latter are built to resist larger amounts of shock. Sony VPCCB2 battery
The exponential increases in disk space and data access speeds of HDDs have enabled consumer products that require large storage capacities, such as digital video recorders and digital audio players.[99] In addition, Sony VPCCB2M0E battery
Sony SVE1511H1EW batterythe availability of vast amounts of cheap storage has made viable a variety of web-based services with extraordinary capacity requirements, such as free-of-charge web search, web archiving, and video sharing (Google, Internet Archive, YouTube, etc.).
Manufacturers and sales[edit source | editbeta]
Sony SVE1511B1EW battery
Diagram of HDD manufacturer consolidation
See also: History of hard disk drives and List of defunct hard disk manufacturers
More than 200 companies have manufactured HDDs over time. But consolidations have concentrated production into just three manufacturers today: Western Digital, Seagate, and Toshiba. Sony VPCCB2M1E battery
Worldwide revenues for HDDs shipments are expected to reach $33 billion in 2013, down about 12% from $37.8 billion in 2012. This corresponds to a 2013 unit shipment forecast of 552 million compared to 577 million units in 2012 and 624 million units in 2011. The estimated 2013 market shares are about 40-45% each for Seagate and Western Digital and 13-16% for Toshiba[100] Sony VPCCB2S1E battery
----------
A solid-state drive (SSD) (also known as a solid-state disk [1][2][3] or electronic disk,[4] though it contains no actual "disk" of any kind, nor motors to "drive" the disks) is a data storage device using integrated circuit assemblies as memory to store data persistently. SSD technology uses electronic interfaces compatible with traditional block input/output (I/O) hard disk drives.
Sony SVE1511S1EW battery
SSDs have no moving mechanical components, which distinguish them from traditional electromechanical magnetic disks such as hard disk drives (HDDs) or floppy disks, which contain spinning disks and movable read/write heads.[5Sony VPCCB3 battery
] Compared with electromechanical disks, SSDs are typically less susceptible to physical shock, run more quietly, have lower access time, and less latency.[6] However, while the price of SSDs has continued to decline in 2012,[7] SSDs are still about 7 to 8 times more expensive per unit of storage than HDDs. VPCCB3P1E battery
Many SSDs use I/O interfaces developed for hard disk drives, thus permitting simple replacement in common applications.[8]
As of 2010, most SSDs use NAND-based flash memory, which retains data without power. For applications requiring fast access, but not necessarily data persistence after power loss, SSDs may be constructed from random-access memory (RAM). Sony VPCCB4X1E battery
Sony VPCCA3E1E battery
Sony SVE1511G1ESI batterySuch devices may employ separate power sources, such as batteries, to maintain data after power loss.[8]
Hybrid drives or solid state hybrid drives (SSHD)[9][10] combine the features of SSDs and HDDs in the same unit, containing a large hard disk drive and an SSD cache to improve performance of frequently accessed data. Sony SVE171A11M battery
Sony SVE1511G1EW batteryThese devices may offer near-SSD performance for many applications.
SSDs had origins in the 1950s with two similar technologies: magnetic core memory and card capacitor read-only store (CCROS).[11][ Sony SVE151C11M battery
Sony SVE1711T1EB battery
Sony SVE1711X1EB battery12] These auxiliary memory units (as contemporaries called them) emerged during the era of vacuum-tube computers. But with the introduction of cheaper drum storage units their use ceased.[13] Sony SVE1711K1EW battery
Sony SVE1711V1EB battery
Later, in the 1970s and 1980s, SSDs were implemented in semiconductor memory for early supercomputers of IBM, Amdahl and Cray;[14] however, the prohibitively high price of the built-to-order SSDs made them quite seldom used. Sony PCG-4R2M battery
In the late 1970s, General Instruments produced an electrically alterable ROM (EAROM) which operated somewhat like the later NAND flash memory. Unfortunately, a ten-year life was not achievable and many companies abandoned the technology.[15] In 1976 Dataram started selling a product called Bulk Core, Sony PCG-4U2M battery
Sony VPCZ12Z9E/X battery which provided up to 2 MB of solid state storage compatible with Digital Equipment Corporation (DEC) and Data General (DG) computers.[16] In 1978, Texas Memory Systems introduced a 16 kilobyte RAM solid-state drive to be used by oil companies for seismic data acquisition.[17] The following year, StorageTek developed the first RAM solid-state drive.[18]
The Sharp PC-5000, introduced in 1983, Sony PCG-6Z4M battery
Sony VPCZ12Z9E/B batteryused 128-kilobyte solid-state storage cartridges containing bubble memory.[19] In 1984 Tallgrass Technologies Corporation had a tape backup unit of 40 MB with a solid state 20 MB unit built in. The 20 MB unit could be used instead of a hard drive.[citation needed] In September 1986, Sony PCG-6121M battery
Sony VPCZ12X9E/B batterySanta Clara Systems introduced BatRam, a 4 megabyte mass storage system expandable to 20 MB using 4 MB memory modules. The package included a rechargeable battery to preserve the memory chip contents when the array was not powered.[20] 1987 saw the entry of EMC Corporation (EMC) Sony PCG-6122M battery
Sony VPCZ12V9E/B battery into the SSD market, with drives introduced for the mini-computer market. However, by 1993 EMC had exited the SSD market.[21][22]
Software-based RAM Disks are still used as of 2009 because they are an order of magnitude faster than the fastest SSD, though they consume CPU resources and cost much more on a per-GB basis.[23] Sony PCG-6123M battery
Flash-based SSDs[edit source | editbeta]
In 1994, STEC, Inc. bought Cirrus Logic's flash controller operation, allowing the company to enter the flash memory business for consumer electronic devices.[citation needed]
In 1995, M-Systems introduced flash-based solid-state drives.[24] They had the advantage of not requiring batteries to maintain the data in the memory (required by the prior volatile memory systems), but were not as fast as the DRAM-based solutions.[2Sony PCG-6124M battery
Sony VPCZ12M9E/B battery5] Since then, SSDs have been used successfully as HDD replacements by the military and aerospace industries, as well as for other mission-critical applications. These applications require the exceptional mean time between failures (MTBF) rates that solid-state drives achieve, by virtue of their ability to withstand extreme shock, vibration and temperature ranges.[26] Sony VPCZ13 battery
In 1999, BiTMICRO made a number of introductions and announcements about flash-based SSDs, including an 18 GB 3.5-inch SSD.[27] In 2007, Fusion-io announced a PCIe-based SSD with 100,000 input/output operations per second (IOPS) of performance in a single card, with capacities up to 320 gigabytes.[28] Sony VPCZ13M9E/B battery
Sony VPCZ12C7E/B battery At Cebit 2009, OCZ Technology demonstrated a 1 terabyte (TB) flash SSD using a PCI Express ×8 interface. It achieved a maximum write speed of 654 megabytes per second (MB/s) and maximum read speed of 712 MB/s.[2Sony VPCZ13V9E battery
Sony VPCZ11Z9E/B battery9] In December 2009, Micron Technology announced the world's first SSD using a 6 gigabits per second (Gbit/s) SATA interface.[30]
Virident Systems came out with the second generation of their flash based SSD in 2012, FlashMAX II. It packs the industry's highest storage capacity into a small form factor: just ½ length x ½ height so it fits in any server with cards allowing up to 2.2 TB of storage. Sony VPCZ13Z9E/X battery
Sony VPCZ11Z9E batteryEven with such a small form factor, these cards can deliver read bandwidth up to 2.7 GB/s and 1.5 million IOPS in a single low-profile card.
Enterprise flash drives[edit source | editbeta] Sony VPCZ21Q9E battery
Enterprise flash drives (EFDs) are designed for applications requiring high I/O performance (IOPS), reliability, energy efficiency and, more recently, consistent performance. In most cases, an EFD is an SSD with a higher set of specifications, compared with SSDs that would typically be used in notebook computers. The term was first used by EMC in January 2008, Sony VPCZ23K9E battery
Sony VPCZ11X9E/B battery to help them identify SSD manufacturers who would provide products meeting these higher standards.[31] There are no standards bodies who control the definition of EFDs, so any SSD manufacturer may claim to produce EFDs when they may not actually meet the requirements.
Sony VPCZ11X9E battery Likewise, there may be other SSD manufacturers that meet the EFD requirements without being called EFDs.[32]
In the fourth quarter of 2012, Intel introduced its SSD DC S3700 drive, which focused on achieving consistent performance, an area that had previously not received much attention but which Intel claimed was important for the enterprise market. In particular, Sony VGP-BPS20/B battery
Intel claims that at steady state the S3700 won't vary its IOPS by more than 10–15%, and that 99.9% of all 4kB random IOs are serviced in less than 500µs.[33]
Architecture and function[edit source | editbeta]
The key components of an SSD are the controller and the memory to store the data. The primary memory component in an SSD had been DRAM volatile memory since they were first developed, but since 2009 it is more commonly NAND flash non-volatile memory.[8][ Sony VGP-BPL14 battery
Sony VGN-Z11VN/X battery34] Other components play a less significant role in the operation of the SSD and vary among manufacturers.[citation needed]
Controller[edit source | editbeta] Sony VGN-Z31 battery
Every SSD includes a controller that incorporates the electronics that bridge the NAND memory components to the host computer. The controller is an embedded processor that executes firmware-level code and is one of the most important factors of SSD performance.[35] Some of the functions performed by the controller include:[36][37] Sony VGN-Z21XN battery
Error correction (ECC)
Wear leveling
Bad block mapping
Read scrubbing and read disturb management
Read and write caching
Garbage collection
Encryption
The performance of an SSD can scale with the number of parallel NAND flash chips used in the device. A single NAND chip is relatively slow, due to the narrow (8/16 bit) asynchronous I/O interface, and additional high latency of basic I/O operations (typical for SLC NAND, Sony VGN-Z31MN/B battery
Sony VGN-Z51WG/B battery~25 μs to fetch a 4K page from the array to the I/O buffer on a read, ~250 μs to commit a 4K page from the IO buffer to the array on a write, ~2 ms to erase a 256 KiB block). When multiple NAND devices operate in parallel inside an SSD, Sony VGN-Z31VN/X battery
Sony VGN-Z51MG/B battery the bandwidth scales, and the high latencies can be hidden, as long as enough outstanding operations are pending and the load is evenly distributed between devices.[38] Micron and Intel initially made faster SSDs by implementing data striping (similar to RAID 0) and interleaving in their architecture. Sony VGN-Z31ZN/B battery
Sony VGN-Z51XTG/B battery This enabled the creation of ultra-fast SSDs with 250 MB/s effective read/write speeds with the SATA 3 Gbit/s interface in 2009.[39] Two years later, SandForce continued to leverage this parallel flash connectivity, releasing consumer-grade SATA 6 Gbit/s SSD controllers which supported 500 MB/s read/write speeds.[40Sony VGN-Z51 battery
] SandForce controllers compress the data prior to sending it to the flash memory. This process may result in less writing and higher logical throughput, depending on the compressibility of the data.[41] Sony VGN-Z51XG battery
Memory[edit source | editbeta]
Flash memory-based[edit source | editbeta]
Most[citation needed] SSD manufacturers use non-volatile NAND flash memory in the construction of their SSDs because of the lower cost compared with DRAM and the ability to retain the data without a constant power supply, Sony VGN-Z battery
Sony VGN-Z41WD/B battery ensuring data persistence through sudden power outages. Flash memory SSDs are slower than DRAM solutions, and some early designs were even slower than HDDs after continued use. This problem was resolved by controllers that came out in 2009 and later.[42]
Comparison of architecture[43] Sony VGP-BPL12 battery
Flash memory-based solutions are typically packaged in standard disk drive form factors (1.8-, 2.5-, and 3.5-inch), or smaller unique and compact layouts because of the compact memory.
Lower priced drives usually use multi-level cell (MLC) flash memory, which is slower and less reliable than single-level cell (SLC) flash memory.[44] Sony PCG-4R2M battery
[45] This can be mitigated or even reversed by the internal design structure of the SSD, such as interleaving, changes to writing algorithms,[45] and higher over-provisioning (more excess capacity) with which the wear-leveling algorithms can work.[46][47][48]
DRAM-based[edit source | editbeta] Sony PCG-4U2M battery
See also: I-RAM and Hyperdrive (storage)
SSDs based on volatile memory such as DRAM are characterized by ultrafast data access, generally less than 10 microseconds, and are used primarily to accelerate applications that would otherwise be held back by the latency of flash SSDs or traditional HDDs. Sony PCG-6112M battery
Sony VPCZ12Z9E/B battery DRAM-based SSDs usually incorporate either an internal battery or an external AC/DC adapter and backup storage systems to ensure data persistence while no power is being supplied to the drive from external sources. If power is lost, the battery provides power while all information is copied from random access memory (RAM) to back-up storage. Sony PCG-6121M battery
Sony VPCZ12X9E/B battery When the power is restored, the information is copied back to the RAM from the back-up storage, and the SSD resumes normal operation (similar to the hibernate function used in modern operating systems).[25] Sony PCG-6122M battery
Sony VPCZ12V9E/B battery [49] SSDs of this type are usually fitted with DRAM modules of the same type used in regular PCs and servers, which can be swapped out and replaced by larger modules.[citation needed] Such as i-RAM, HyperOs HyperDrive, Sony PCG-6124M battery
DDRdrive X1, etc. Some manufacturers of DRAM SSDs solder the DRAM chips directly to the drive, and do not intend the chips to be swapped out—such as ZeusRAM, Aeon Drive, etc.[50]
A remote, indirect memory-access disk (RIndMA Disk) uses a secondary computer with a fast network or (direct) Infiniband connection to act like a RAM-based SSD, but the new, faster, flash-memory based, SSDs already available in 2009 are making this option not as cost effective.[51] Sony VPCZ13M9E/B battery
While the price of DRAM continues to fall, the price of Flash memory falls even faster. The "Flash becomes cheaper than DRAM" crossover point occurred approximately 2004.[52][53]
Other[edit source | editbeta] Sony VPCZ13V9E battery
Some SSDs use MRAM.[54][55]
Some SSDs use both DRAM and flash memory. When the power goes down, the SSD copies all the data from its DRAM to flash. When the power comes back up, the SSD copies all the data from its flash to its DRAM.[56]
Some drives use a hybrid of spinning disks and flash memory.[57][58]
Cache or buffer[edit source | editbeta] Sony VPCZ21Q9E battery
A flash-based SSD typically uses a small amount of DRAM as a cache, similar to the cache in hard disk drives. A directory of block placement and wear leveling data is also kept in the cache while the drive is operating. Data is not permanently stored in the cache.[38] Sony VPCZ23K9E battery
One SSD controller manufacturer, SandForce, does not use an external DRAM cache on their designs, but still achieves very high performance. Eliminating the external DRAM enables a smaller footprint for the other flash memory components in order to build even smaller SSDs.[59]
Battery or super capacitor[edit source | editbeta] Sony VGP-BPS20/B battery
Another component in higher performing SSDs is a capacitor or some form of battery. These are necessary to maintain data integrity such that the data in the cache can be flushed to the drive when power is dropped; some may even hold power long enough to maintain data in the cache until power is resumed.[citation needed] Sony VGP-BPS20/S battery
Sony VPCZ11Z9E/B battery In the case of MLC flash memory, a problem called lower page corruption can occur when MLC flash memory loses power while programming an upper page. The result is that data written previously and presumed safe can be corrupted if the memory is not supported by a super capacitor in the event of a sudden power loss. This problem does not exist with SLC flash memory.[37]
Sony VPCZ11Z9E battery Most consumer-class SSDs do not have built-in batteries or capacitors;[60] among the exceptions are the Crucial M500 series,[61] the Intel 320 series[62] and the more expensive Intel 710 series.[63] Sony VPCZ11 battery
Host interface[edit source | editbeta]
The host interface is not specifically a component of the SSD, but it is a key part of the drive. The interface is usually incorporated into the controller discussed above. The interface is generally one of the interfaces found in HDDs. They include: Sony VPCZ11X9E battery
The size and shape of any device is largely driven by the size and shape of the components used to make that device. Traditional HDDs and optical drives are designed around the rotating platter or optical disc along with the spindle motor inside. If an SSD is made up of various interconnected integrated circuits (ICs) and an interface connector, Sony VGP-BPL14 battery
then its shape could be virtually anything imaginable because it is no longer limited to the shape of rotating media drives. Some solid state storage solutions come in a larger chassis that may even be a rack-mount form factor with numerous SSDs inside. They would all connect to a common bus inside the chassis and connect outside the box with a single connector.[8]
For general computer use, the 2.5-inch form factor (typically found in laptops) is the most popular. For desktop computers with 3.5-inch hard disk slots, a simple adapter plate can be used to make such a disk fit. Sony VGP-BPL14/S battery
Sony VGN-Z51XG/B batteryOther type of form factors are more common in enterprise applications. An SSD can also be completely integrated in the other circuitry of the device, as in the Apple MacBook Air (starting with the fall 2010 model).[citation needed] Sony VGP-BPS14 battery
Standard HDD form factors[edit source | editbeta]
The benefit of using a current HDD form factor would be to take advantage of the extensive infrastructure already in place to mount and connect the drives to the host system.[8][67] These traditional form factors are known by the size of the rotating media, e.g., 5.25-inch, 3.5-inch, 2.5-inch, 1.8-inch, not by the dimensions of the drive casing.[68] Sony VGP-BPS14/S battery
Box form factors[edit source | editbeta]
Many of the DRAM-based solutions use a box that is often designed to fit in a rack-mount system. The number of DRAM components required to get sufficient capacity to store the data along with the backup power supplies requires a larger space than traditional HDD form factors.[citation needed] Sony VGN-Z11WN/B battery
Form factors which were more common to memory modules are now being used by SSDs to take advantage of their flexibility in laying out the components. Some of these include PCIe, mini PCIe, mini-DIMM, MO-297, and many more.[ Sony VGN-Z11XN/X battery
Sony VGN-Z51MG/B battery69] The SATADIMM from Viking Technology uses an empty DDR3 DIMM slot on the motherboard to provide power to the SSD with a separate SATA connector to provide the data connection back to the computer. Sony VGN-Z21 battery
Sony VGN-Z51XTG/B batteryThe result is an easy-to-install SSD with a capacity equal to drives that typically take a full 2.5-inch drive bay.[70] At least one manufacturer, Innodisk, has produced a drive that sits directly on the SATA connector (SATADOM) Sony VGN-Z21MN/B battery
Sony VGN-Z31XN/B battery on the motherboard without any need for a power cable.[71] Some SSDs are based on the PCIe form factor and connect both the data interface and power through the PCIe connector to the host. These drives can use either direct PCIe flash controllers[72] or a PCIe-to-SATA bridge device which then connects to SATA flash controllers.[73] Sony VGN-Z21XN battery
Ball grid array form factors[edit source | editbeta]
In the early 2000s, a few companies introduced SSDs in Ball Grid Array (BGA) form factors, such as M-Systems' (now SanDisk) DiskOnChip[74] and Silicon Storage Technology's NANDrive[75][76] (now produced by Greenliant Systems), Sony VGN-Z31 battery
Sony VGN-Z41WD/B batteryand Memoright's M1000[77] for use in embedded systems. The main benefits of BGA SSDs are their low power consumption, small chip package size to fit into compact subsystems, and that they can be soldered directly onto a system motherboard to reduce adverse effects from vibration and shock.[78] Sony VGN-Z31VN/X battery
Comparison of SSD with hard disk drives[edit source | editbeta]
See also: Hard disk drive performance characteristics
SSD benchmark, showing about 230 MB/s reading speed (blue), 210 MB/s writing speed (red) and about 0.1 ms seek time (green), all independent from the accessed disk location.
Making a comparison between SSDs and ordinary (spinning) HDDs is difficult. Sony VGN-Z31WN/B battery
Sony VGP-BPS12 batteryTraditional HDD benchmarks tend to focus on the performance characteristics that are poor with HDDs, such as rotational latency and seek time. As SSDs do not need to spin or seek to locate data, they may prove vastly superior to HDDs in such tests. However, SSDs have challenges with mixed reads and writes,
Sony VGP-BPL12 battery and their performance may degrade over time. SSD testing must start from the (in use) full disk, as the new and empty (fresh out of the box) disk may have much better write performance than it would show after only weeks of use.[79] Sony VGN-Z31ZN/B battery
Most of the advantages of solid-state drives over traditional hard drives are due to their ability to access data completely electronically instead of electromechanically, resulting in superior transfer speeds and mechanical ruggedness.[80] On the other hand, hard disk drives offer significantly higher capacity for their price.[6][81] Sony VGN-Z51 battery
While SSDs appear to be more reliable than HDDs,[82][83] SSD failures are often catastrophic, with total data loss. As of 2013, most SSDs fail poorly on power faults.[84] While HDDs can fail in this manner as well, they often give warning that they are failing, allowing much or all of their data to be recovered.[85] Sony VGN-Z51WG battery
Sony VGN-Z51XG battery Additionally, the robustness of an SSD varies greatly amongst models.
Not all solid-state drives perform equally. Single-level cell (SLC) SSDs have faster access times than multi-level cell (MLC) SSDs. DRAM-based solid-state storage is currently considered the fastest, with average response times of 10 microseconds instead of the average 100 microseconds of other SSDs. Sony vgp-bps24 battery
Sony SVS1511T9ES battery Enterprise flash devices (EFDs) are designed to handle the demands of Tier-1 application with performance and response times similar to less-expensive SSDs.[86]
Traditional hard drives store their data in a linear, ordered manner. SSDs, however, constantly rearrange their data while keeping track of their locations for the purpose of wear leveling.
Sony SVS1511N3ES batteryAs such, the flash memory controller and its firmware play a critical role in maintaining data integrity. One major cause of data loss in SSDs is firmware bugs,[87] which rarely cause problems in HDDs.[dubious – discuss][88] Sony vgp-bpsc24 battery
Sony VPCSD1S1C battery
The following table shows a detailed overview of the advantages and disadvantages of both technologies. Comparisons reflect typical characteristics, and may not hold for a specific device.
Attribute or characteristic Solid-state drive Hard disk drive Sony SVS15 battery
Sony VPCSA2Z9E battery
Start-up time Almost instantaneous; no mechanical components to prepare. May need a few milliseconds to come out of an automatic power-saving mode. Disk spin-up may take several seconds. A system with many drives may need to stagger spin-up to limit peak power drawn, which is briefly high when an HDD is first started.[citation needed] Sony SVE171A11M battery
Sony SVE151C11M battery
Random access time[89] Typically under 100 µs.[90] As data can be retrieved directly from various locations of the flash memory, access time is usually not a big performance bottleneck. Ranges from 2.9 (high end server drive) to 12 ms (laptop HDD) due to the need to move the heads and wait for the data to rotate under the read/write head[91] Sony SVE1711T1EB battery
Sony SVE1711K1EW battery
Read latency time[92] Generally low because the data can be read directly from any location. In applications where hard disk seeks are the limiting factor, this results in faster boot and application launch times (see Amdahl's law).[93] Much higher than SSDs. Read time is different for every different seek, since the location of the data on the disk and the location of the read-head make a difference. Sony SVE1711V1EB battery
Data transfer rate SSD technology can deliver rather consistent read/write speed, but when lots of individual smaller blocks are accessed, performance is reduced. In consumer products the maximum transfer rate typically ranges from about 100 MB/s to 600 MB/s, Sony SVE1711X1EB battery
Sony SVS1311P9EB batterydepending on the disk. Enterprise market offers devices with multi-gigabyte per second throughput. Once the head is positioned, when reading or writing a continuous track, an enterprise HDD can transfer data at about 140 MB/s. Sony SVE1511G1EW battery
Sony SVE1511G1ESI battery
Sony SVS1311E3EW battery In practice transfer speeds are many times lower due to constant seeking, as files are read from various locations or they are fragmented. Data transfer rate depends also upon rotational speed, which can range from 4,200 to 15,000 rpm.[ Sony SVE1511G1EB battery
Sony SVE1511S1EW battery
Sony SVS151A12M battery94] and also upon the track (reading from the outer tracks is faster due higher absolute head velocity relative to the disk).
Read performance[95] Read performance does not change based on where data is stored on an SSD.[citation needed] Sony SVE1511S1ESI battery
Unlike mechanical hard drives, current SSD technology suffers from a performance degradation phenomenon called write amplification, where the NAND cells show a measurable drop in performance, and will continue degrading throughout the life of the SSD. Sony SVE1511S1EB battery
Sony SVE1511B1EW battery
Sony SVS151A11M batteryA technique called wear leveling is implemented to mitigate this effect, but due to the nature of the NAND chips, the drive will inevitably degrade at a noticeable rate.
If data from different areas of the platter must be accessed, as with fragmented files, response times will be increased by the need to seek each fragment[citation needed] Sony SVE1511H1EW battery
Fragmentation (filesystem specific) There is limited benefit to reading data sequentially (beyond typical FS block sizes, say 4kB), making fragmentation negligible for SSDs.[96] Defragmentation would cause wear by making additional writes of the NAND flash cells, which have a limited cycle life.[97][98] Sony SVE1511H1ESI battery
Sony SVS131B12M battery Files, particularly large ones, on HDDs usually become fragmented over time if frequently written; periodic defragmentation is required to maintain optimum performance.
Sony SVS13AA11M battery
Noise (acoustic)[100] SSDs have no moving parts and therefore are basically silent, although electric noise from the circuits may occur. HDDs have moving parts (heads, actuator, and spindle motor) and make characteristic sounds of whirring and clicking; noise levels vary between models, but can be significant (while often much lower than the sound from the cooling fans). Laptop hard disks are relatively quiet. [99] Sony SVE1511J1EW battery
Temperature control[101] SSDs do not usually require any special cooling and can tolerate higher temperatures than HDDs. High-end enterprise models delivered as add-on cards may be supplied fitted with heat sinks to dissipate heat generated. According to Seagate, ambient temperatures above 95 °F (35 °C) Sony VPCCA4S1E battery
Sony VPCCA2S1E batterycan shorten the life of a hard disk, and reliability will be compromised at drive temperatures above 131 °F (55 °C). Fan cooling may be required if temperatures would otherwise exceed these values.[102] In practice most hard drives are used without special arrangements for cooling. Sony VPCCB3M1E battery
Sony VPCCA3S1E battery
Susceptibility to environmental factors[93][103][104] No moving parts, very resistant to shock and vibration Heads floating above rapidly rotating platters are susceptible to shock and vibration
Sony PCG-4121GM battery
Installation and mounting Not sensitive to orientation, vibration, or shock. Usually no exposed circuitry. Circuitry may be exposed, and must not contact metal parts. Most recent models work well in all orientations.[citation needed] Should be mounted to protect against vibration and shock.
Sony PCG-41214M battery
Susceptibility to magnetic fields [105] Low impact on flash memory. But an electromagnetic pulse (EMP) will damage any electrical system, especially integrated circuits. Magnets or magnetic surges could in principle damage data, although the magnetic platters are usually well-shielded inside a metal case. Sony SVS1511V9EB battery
Weight and size[103] Solid state drives, essentially semiconductor memory devices mounted on a circuit board, are small and light in weight. However, for easy replacement, they often follow the same form factors as HDDs (3.5-inch, 2.5-inch or 1.8-inch). Such form factors typically weigh as much as their HDD counterparts, mostly due to the enclosure. Sony SVS1511V9ES battery
Sony SVS1511W9EB battery
Sony PCG-41218M battery HDDs typically have the same form factor but may be heavier. This applies for 3.5-inch drives, which typically weigh around 700 grams.
Reliability and lifetime SSDs have no moving parts to fail mechanically. Each block of a flash-based SSD can only be erased (and therefore written) a limited number of times before it fails. The controllers manage this limitation so that drives can last for many years under normal use.[106][107][108][1Sony VPCSA3Q9E battery
Sony VPCSB4S9E battery
Sony PCG-41213M battery09][110] SSDs based on DRAM do not have a limited number of writes. However the failure of a controller can make a SSD unusable. Reliability varies significantly across different SSD manufacturers and models.
Sony PCG-41211M battery HDDs have moving parts, and are subject to potential mechanical failures from the resulting wear and tear. The storage medium itself (magnetic platter) does not essentially degrade from read and write operations. Sony VPCSE2F1E battery
According to a study performed by Carnegie Mellon University for both consumer and enterprise-grade HDDs, their average failure rate is 6 years, and life expectancy is 9 – 11 years.[111] Sony VPCSE2V9E battery
Sony PCG-4121DM battery
The reliability of hard disks is much more consistent than of SSDs. The risk of a sudden, catastrophic data loss is also lower.
Secure writing limitations NAND flash memory cannot be overwritten, but has to be rewritten to previously erased blocks. If a software encryption program encrypts data already on the SSD, the overwritten data is still unsecured, unencrypted, Dell XPS 14 battery
Dell XPS M2010 battery and accessible (drive-based hardware encryption does not have this problem). Also data cannot be securely erased by overwriting the original file without special "Secure Erase" procedures built into the drive.[11Dell XPS 15 battery
Dell XPS M1730 battery2] HDDs can overwrite data directly on the drive in any particular sector. However the drive's firmware may exchange damaged blocks with spare areas, so bits and pieces may still be present. Dell XPS 17 battery
Cost per capacity NAND flash SSDs have reached US$0.59 per GB [113] HDDs cost about US$0.05 per GB for 3.5-inch and $0.10 per GB for 2.5-inch drives
Storage capacity[needs update] In 2011 SSDs were available in sizes up to 2 TB, but less costly 64 to 256 GB drives were more common.[citation needed] In 2011 HDDs of up to 4 TB were available.[citation needed] Dell XPS L401X battery
Read/write performance symmetry Less expensive SSDs typically have write speeds significantly lower than their read speeds. Higher performing SSDs have similar read and write speeds. HDDs generally have slightly lower write speeds than their read speeds.[citation needed]
Dell XPS M1330 battery
Free block availability and TRIM SSD write performance is significantly impacted by the availability of free, programmable blocks. Previously written data blocks no longer in use can be reclaimed by TRIM; however, even with TRIM, fewer free blocks cause slower performance.[38][114][1Dell XPS L501X battery
Dell XPS M1210 battery15] HDDs are not affected by free blocks and do not benefit from TRIM
Power consumption High performance flash-based SSDs generally require half to a third of the power of HDDs. High-performance DRAM SSDs generally require as much power as HDDs, and must be connected to power even when the rest of the system is shut down.[116][117] The lowest-power HDDs (1.8-inch size) can use as little as 0.35 watts.[ Dell XPS L502X battery
Dell XPS L701X battery
Dell XPS L702X battery118] 2.5-inch drives typically use 2 to 5 watts. The highest-performance 3.5-inch drives can use up to about 20 watts.
Comparison of SSDs with memory cards[edit source | editbeta]
CompactFlash card used as an SSD
While both memory cards and most SSDs use flash memory, they serve very different markets and purposes. Each has a number of different attributes which are optimized and adjusted to best meet the needs of particular users. Some of these characteristics include power consumption, performance, size, and reliability.[119] Dell Latitude E4200 battery
Dell Latitude E5520 battery
SSDs were originally designed for use in a computer system. The first units were intended to replace or augment hard disk drives, so the operating system recognized them as a hard drive. Originally, solid state drives were even shaped and mounted in the computer like hard drives. Later SSDs became smaller and more compact, Dell Latitude E5400 battery
Dell Latitude E5420 batteryeventually developing their own unique form factors. The SSD was designed to be installed permanently inside a computer.[119]
In contrast, memory cards (such as Secure Digital (SD), CompactFlash (CF) and many others) were originally designed for digital cameras and later found their way into cell phones, gaming devices, GPS units, etc. Most memory cards are physically smaller than SSDs, and designed to be inserted and removed repeatedly.[1Dell Latitude E5410 battery
Dell Latitude E5220 battery19] There are adapters which enable some memory cards to interface to a computer, allowing use as an SSD, but they are not intended to be the primary storage device in the computer. The typical CompactFlash card interface is three to four times slower than an SSD. Dell Latitude E5510 battery
Dell Latitude E6430s batteryAs memory cards are not designed to tolerate the amount of reading and writing which occurs during typical computer use, their data may get damaged unless special procedures are taken to reduce the wear on the card to a minimum. Dell Latitude E5500 battery
Dell Latitude E6400 battery
Applications[edit source | editbeta]
Until 2009, SSDs were mainly used in those aspects of mission critical applications where the speed of the storage system needed to be as fast as possible. Since flash memory has become a common component of SSDs, Dell Latitude E6400 ATG battery
Dell Latitude E6430 battery the falling prices and increased densities have made it more cost-effective for many other applications. Organizations that can benefit from faster access of system data include equity trading companies, telecommunication corporations, streaming media and video editing firms. The list of applications which could benefit from faster storage is vast.[8] Dell Latitude E6500 battery
Dell Latitude E6330 battery
Flash-based solid-state drives can be used to create network appliances from general-purpose personal computer hardware. A write protected flash drive containing the operating system and application software can substitute for larger, less reliable disk drives or CD-ROMs. Appliances built this way can provide an inexpensive alternative to expensive router and firewall hardware.[citation needed] Dell Latitude E4300 battery
Dell Latitude E6320 battery
SSDs based on an SD card with a live SD operating system are easily write-locked. Combined with a cloud computing environment or other writable medium, to maintain persistence, an OS booted from a write-locked SD card is robust, rugged, reliable, and impervious to permanent corruption. If the running OS degrades, Dell Latitude E4310 battery
Dell Latitude E6230 batterysimply turning the machine off and then on returns it back to its initial uncorrupted state and thus is particularly solid. The SD card installed OS does not require removal of corrupted components since it was write-locked though any written media may need to be restored.
Dell Latitude E6220 battery
In 2011, Intel introduced a caching mechanism for their Z68 chipset (and mobile derivatives) called Smart Response Technology, which allows a SATA SSD to be used as a cache (configurable as write-through or write-back) for a conventional, magnetic hard disk drive.[120] A similar technology is available on HighPoint's RocketHybrid PCIe card.[121Dell Latitude E4320 battery
Dell Latitude E6400 XFR battery
] Hybrid drives (H-HDSs) are based on the same principle, but integrate some amount of flash memory on board of a conventional drive instead of using a separate SSD. The flash layer in these drives can be accessed independently from the magnetic storage by the host using ATA-8 commands, Dell Latitude E6410 battery
Dell Latitude E6210 batteryallowing the operating system to manage it. For example Microsoft's ReadyDrive technology explicitly stores portions of the hibernation file in the cache of these drives when the system hibernates, making the subsequent resume faster.[122]
Data recovery and secure deletion[edit source | editbeta]
Dell Latitude E6410 ATG battery
Solid state drives have set new challenges for data recovery companies, as the way of storing data is non-linear and much more complex than that of hard disk drives. The strategy the drive operates by internally can largely vary between manufacturers and, Dell Latitude E6500 battery
Dell Latitude E6510 battery
Dell Latitude E6120 batterythe TRIM command zeroes the whole range of a deleted file. Wear leveling also means that the physical address of the data and the address exposed to the operating system are different.
As for secure deletion of data, using the ATA Secure Erase command is recommended, as the drive itself knows the most effective method to truly reset its data. A program such as Parted Magic can be used for this purpose.[123] Sony PCG-4R2M battery
File systems suitable for SSDs[edit source | editbeta]
Main article: File systems optimized for flash memory, solid state media
Typically the same file systems used on hard disk drives can also be used on solid state disks. It is usually expected for the file system to support the TRIM command which helps the SSD to recycle discarded data. Sony PCG-4U2M battery
Sony VPCZ12Z9E/X batteryThere is no need for the file system to take care of wear leveling or other flash memory characteristics, as they are handled internally by the SSD. Some flash file systems using log-based designs (F2FS, JFFS2) help to reduce write amplification on SSDs, especially in situations where only very small amounts of data are changed, such as when updating file system metadata. Sony PCG-6Z4M battery
While not a file system feature, operating systems must also align partitions correctly to avoid excessive read-modify-write cycles. Other features designed for hard disk drives, most notably defragmentation, are disabled in SSD installations.
Listed below are some notable computer file systems that work well with solid-states drives.
Linux systems[edit source | editbeta] Sony PCG-6112M battery
The ext4, Btrfs and F2FS file systems include support for the discard (TRIM) function. Currently ext4 can be recommended as a safe choice. F2FS is a modern file system optimized for flash-based storage, and is a very good choice, but is still in experimental stage. Kernel support for the TRIM function was introduced in version 2.6.33. Sony PCG-6122M battery
Sony VPCZ12Z9E/B batteryTo make use of it, the filesystem must be mounted using the discard parameter. Linux distributions usually do not set this kind of configuration automatically during installation[124] and thus the fstab file requires manual modification. This is because of the notion that the current Linux TRIM command implementation might not be optimal.[12Sony PCG-6124M battery
Sony VPCZ12X9E/B battery5] It has been proven to cause a performance degradation instead of a performance increase under certain circumstances.[126][127] The disk utilities take care of proper partition alignment.[128] Sony VPCZ13 battery
Mac OS X[edit source | editbeta]
Mac OS X versions since 10.6.8 (Snow Leopard) support TRIM but only when used with an Apple-purchased SSD.[129] There is also a technique to enable TRIM in earlier versions, though it is uncertain whether TRIM is utilized properly if enabled in versions before 10.6.8.[13
Sony VPCZ12V9E battery0] TRIM is generally not automatically enabled for third-party drives, although it can be enabled by using third-party utilities such as Trim Enabler. The status of TRIM can be checked in the System Information application or in the system_profiler command-line tool.
Microsoft Windows[edit source | editbeta]
Versions of Microsoft Windows prior to Vista do not take any special measures to support solid state drives. Partitions can be manually aligned before OS installation. Defragmentation negatively affects the life of the SSD and has no benefit. The TRIM command can be triggered using third-party tools to help maintain performance over time. Sony VPCZ13M9E/B battery
Starting from Windows 7, the standard NTFS file system provides TRIM support (other file systems do not support TRIM[131]).
By default Windows 7 and Windows 8 execute TRIM commands automatically if the device is detected to be a solid-state drive. To reverse this, in the registry key Sony VPCZ13V9E battery
Sony VPCZ12C7E/B batterycan be set to 1 to prevent the mass storage driver from issuing the TRIM command. This can be useful in situations where data recovery is preferred over wear leveling (TRIM irreversibly resets all data that it manipulates). Sony VPCZ13Z9E/X battery
Windows 7 and 8[edit source | editbeta]
Windows 7 has support for SSDs.[132][133] Support in Windows 8 is similar. The operating system detects the presence of an SSD and optimizes operation accordingly. For SSD devices Windows disables defragmentation, Superfetch and ReadyBoost, which are boot-time and application prefetching operations. Sony VPCZ21Q9E battery
Sony VPCZ11Z9E batteryIt also includes support for the TRIM command to reduce garbage collection for data which the operating system has already determined is no longer valid. Without support for TRIM, the SSD would be unaware of this data being invalid and would unnecessarily continue to rewrite it during garbage collection causing further wear on the SSD.[134][135] Sony VPCZ23K9E battery
Windows Vista[edit source | editbeta]
Windows Vista generally expects hard disk drives rather than SSDs.[136][137] Windows Vista includes ReadyBoost to exploit characteristics of USB-connected flash devices, but for SSDs it only improves the default partition alignment to prevent read-modify-write operations which reduce the speed of the SSD. Sony VGP-BPL20 battery
Sony VPCZ11X9E batteryThis is because most SSDs are typically aligned on 4 kB sectors and most systems are based on 512 byte sectors with the default partition set up unaligned.[138] The proper alignment really does not help the SSD's endurance over the life of the drive, however some Vista operations, Sony VGP-BPS20/B battery
if not disabled, can shorten the life of the SSD. Disk defragmentation should be disabled because the location of the file components on an SSD doesn't significantly impact its performance, but moving the files to make them contiguous using the Windows Defrag routine will cause unnecessary write wear on the limited number of P/E cycles on the SSD. Sony VGP-BPS20/S battery
Sony VPCZ11 battery The Superfetch feature will not materially improve the performance of the system and causes additional overhead in the system and SSD, although it does not cause wear.[139] There is no official information to confirm whether Windows Vista sends TRIM commands to a solid state drive. Sony VGP-BPL14 battery
ZFS[edit source | editbeta]
Solaris as of version 10 Update 6 (released in October 2008), and recent versions of OpenSolaris, Solaris Express Community Edition, Illumos, Linux with ZFS on Linux and FreeBSD all can use SSDs as a performance booster for ZFS. A low-latency SSD can be used for the ZFS Intent Log (ZIL), where it is named the SLOG. Sony VGP-BPL14/S battery
This is used every time a synchronous write to the disk occurs. An SSD (not necessarily with a low-latency) may also be used for the level 2 Adaptive Replacement Cache (L2ARC), which is used to cache data for reading. When used either alone or in combination, large increases in performance are generally seen.[140] Sony VGP-BPS14 battery
FreeBSD[edit source | editbeta]
In addition to the ZFS features described above, the Unix File System (UFS) supports the TRIM command.
Swap partitions[edit source | editbeta]
On Linux, swap partitions automatically exploit TRIM operations when the underlying drive supports TRIM (no configuration is needed).[141][142] Sony VGP-BPS14/S battery
If an operating system does not support using TRIM on discrete swap partitions, it might be possible to use swap files inside an ordinary file system instead.
DragonFly BSD allows SSD-configured swap to also be used as file system cache.[143] This can be used to boost performance on both desktop and server workloads. The bcache, dm-ssdcache, EnhanceIO and tier projects provide a similar concept for the Linux kernel. Sony VGN-Z11WN/B battery
Standardization organizations[edit source | editbeta]
The following are noted standardization organizations and bodies that work to create standards for solid-state drives (and other computer storage devices). The table below also includes organizations which promote the use of solid-state drives. This is not necessarily an exhaustive list. Sony VGN-Z11XN/X battery
Solid-state drive technology has been marketed to the military and niche industrial markets since the mid-1990s.[citation needed].
Along with the emerging enterprise market, SSDs have been appearing in ultra-mobile PCs and a few lightweight laptop systems, adding significantly to the price of the laptop, depending on the capacity, form factor and transfer speeds. Sony VGP-BPL14 battery
Sony VGP-BPS12/Q battery For low-end applications, a USB flash drive may be obtainable for anywhere from $10 to $100 or so, depending on capacity; alternatively, a CompactFlash card may be paired with a CF-to-IDE or CF-to-SATA converter at a similar cost. Sony VGP-BPL14/S battery
Sony VGP-BPS12 batteryEither of these requires that write-cycle endurance issues be managed, either by refraining from storing frequently written files on the drive or by using a flash file system. Standard CompactFlash cards usually have write speeds of 7 to 15 MB/s while the more expensive upmarket cards claim speeds of up to 60 MB/s. Sony VGP-BPS14/B battery
One of the first mainstream releases of SSD was the XO Laptop, built as part of the One Laptop Per Child project. Mass production of these computers, built for children in developing countries, began in December 2007. Sony VGP-BPS14/S battery
These machines use 1,024 MiB SLC NAND flash as primary storage which is considered more suitable for the harsher than normal conditions in which they are expected to be used. Dell began shipping ultra-portable laptops with SanDisk SSDs on April 26, 2007.[144] Asus released the Eee PC subnotebook on October 16, Sony VGN-Z11WN/B battery
Sony VGN-Z battery2007, with 2, 4 or 8 gigabytes of flash memory.[145] On January 31, 2008, Apple released the MacBook Air, a thin laptop with an optional 64 GB SSD. The Apple Store cost was $999 more for this option, Sony VGN-Z11XN/X battery
Sony VGN-Z51XG battery as compared with that of an 80 GB 4200 RPM hard disk drive.[146] Another option, the Lenovo ThinkPad X300 with a 64 gigabyte SSD, was announced by Lenovo in February 2008.[147] On August 26, 2008, Lenovo released ThinkPad X301 with 128 GB SSD option which adds approximately $200 US.[citation needed] Sony VGN-Z21 battery
The Mtron SSD
In 2008 low end netbooks appeared with SSDs. In 2009 SSDs began to appear in laptops.[144][146]
On January 14, 2008, EMC Corporation (EMC) became the first enterprise storage vendor to ship flash-based SSDs into its product portfolio when it announced it had selected STEC, Inc.'s Zeus-IOPS SSDs for its Symmetrix DMX systems.[148] Sony VGN-Z21MN/B battery
In 2008 Sun released the Sun Storage 7000 Unified Storage Systems (codenamed Amber Road), which use both solid state drives and conventional hard drives to take advantage of the speed offered by SSDs and the economy and capacity offered by conventional hard disks.[149] Sony VGN-Z21WN/B battery
Dell began to offer optional 256 GB solid state drives on select notebook models in January 2009.[citation needed]
In May 2009, Toshiba launched a laptop with a 512 GB SSD.[150][151]
Since October 2010, Apple's MacBook Air line has used a solid state drive as standard.[152]
In December 2010, OCZ RevoDrive X2 PCIe SSD was available in 100 GB to 960 GB capacities delivering speeds over 740 MB/s sequential speeds and random small file writes up to 120,000 IOPS.[153]
In November 2010, Fusion-io released its highest performing SSD drive named ioDrive Octal utilising PCI-Express x16 Gen 2.0 interface with storage space of 5.12 TB, read speed of 6.0 GB/s, write speed of 4.4 GB/s and a low latency of 30 microseconds. It has 1.19 M Read 512 byte IOPS and 1.18 M Write 512 byte IOPS.[154] Sony VGN-Z21ZN/X battery
In 2011, computers based on Intel's Ultrabook specifications became available. These specifications dictate that Ultrabooks use an SSD. These are consumer-level devices (unlike many previous flash offerings aimed at enterprise users), and represent the first widely available consumer computers using SSDs aside from the MacBook Air.[citation needed] Sony VGN-Z31MN/B battery
At CES 2012, OCZ Technology demonstrated the R4 CloudServ PCIe SSDs capable of reaching transfer speeds of 6.5 GB/s and 1.4 million IOPS.[155] Also announced was the Z-Drive R5 which is available in capacities up to 12 TB capable of reaching transfer speeds of 7.2 GB/s and 2.52 million IOPS using the PCI Express x16 Gen 3.0.[156] Sony VGN-Z31VN/X battery
Quality and performance[edit source | editbeta]
Main article: Disk drive performance characteristics
SSD technology has been developing rapidly. Sony VGN-Z51MG/B battery
Most of the performance measurements used on disk drives with rotating media are also used on SSDs. Performance of flash-based SSDs is difficult to benchmark because of the wide range of possible conditions. In a test performed in 2010 by Xssist, using IOmeter,
Sony VGN-Z11VN/X battery 4 kB random 70% read/30% write, queue depth 4, the IOPS delivered by the Intel X25-E 64 GB G1 started around 10,000 IOPs, and dropped sharply after 8 minutes to 4,000 IOPS, and continued to decrease gradually for the next 42 minutes. IOPS vary between 3,000 to 4,000 from around 50 minutes onwards for the rest of the 8+ hour test run.[15
7]
Write amplification is the major reason for the change in performance of an SSD over time. Designers of enterprise-grade drives try to avoid this performance variation by increasing over provisioning, and by employing wear-leveling algorithms that move data only when the drives are not heavily utilized.[158] Sony VGN-Z41WD/B battery
Sales[edit source | editbeta]
SSD shipments were 11 million units in 2009,[159] 17.3 million units in 2011[160] for a total of $5 billion,[161] 39 million units in 2012, and are expected to rise to 83 million units in 2013[162] to 201.4 million units in 2016[160] and to 227 million units in 2017.[163] Sony VGN-Z31XN/B battery
Revenues for the SSD market (including low-cost PC solutions) worldwide totaled US$585 million in 2008, rising over 100% from US$259 million in 2007.[164]