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Solid-state drive

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This article is about flash-based, DRAM-based, and other solid-state storage. For removable USB solid-state storage, see USB flash drive. For compact flash memory cards, see memory card. For software-based secondary storage, see RAM disk.
"Electronic disk" redirects here. For other uses, see Electronic disk (disambiguation).
"SSD" redirects here. For other uses, see SSD (disambiguation).
An SSD in standard 2.5-inch (64 mm) form-factor
DDR SDRAM based SSD. Max 128 GB and 3072 MB/s.
File:Hp-io-accelerator-isometric.gif
PCI attached IO Accelerator SSD
PCI-E, DRAM, and NAND based SSD

A solid-state drive (SSD), sometimes called a solid-state disk or electronic disk, is a data storage device that uses integrated circuit assemblies as memory to store data persistently. SSD technology uses electronic interfaces compatible with traditional block I/O hard disk drives. SSDs do not employ any moving mechanical components, which distinguishes them from traditional magnetic disks such as hard disk drives (HDDs) or floppy disk, which are electromechanical devices containing spinning disks and movable read/write heads.[1] Compared to electromechanical disks, SSDs are typically less susceptible to physical shock, are silent, and have lower access time and latency, but are, at present market prices, more expensive per unit of storage.

SSDs share the input/output interface technology developed for hard disk drives, thus permitting simple replacement for most applications.[2]

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). Such devices may employ separate power sources, such as batteries, to maintain data after power loss.[2]

Hybrid drives combine the features of SSD and HDD in the same unit, containing a large hard disk and an SSD cache to improve performance of frequently accessed data. These devices may offer near-SSD performance for many applications.

Development and history

Early SSDs using RAM and similar technology

The origins of SSDs came from the 1950s using two similar technologies, magnetic core memory and card capacitor read-only store (CCROS).[3][4] These auxiliary memory units, as they were called at the time, emerged during the era of vacuum tube computers. But with the introduction of cheaper drum storage units, their use was discontinued.[5]

Later, in the 1970s and 1980s, SSDs were implemented in semiconductor memory for early supercomputers of IBM, Amdahl and Cray;[6] however, the prohibitively high price of the built-to-order SSDs made them quite seldom used. In the late 1970s, General Instruments produced an electrically alterable ROM (EAROM) which operated somewhat like the later NAND flash memory. But a 10-year life was not achievable, and many companies abandoned the technology.[7] In 1976 Dataram started selling a product called BULK CORE, which provided up to 2MB of solid state storage compatible with DEC and Data General computers.[8] In 1978, Texas Memory Systems introduced a 16 kilobyte (KB) RAM solid-state drive, to be used by oil companies for seismic data acquisition.[9] The following year, StorageTek developed the first modern type of solid-state drive.[10]

The Sharp PC-5000, introduced in 1983, used 128 kilobyte solid-state storage cartridges, containing bubble memory.[11] In 1984 Tallgrass Technologies Corporation had a tape back up 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, Santa Clara Systems introduced BatRam, a 4 megabyte (MB) 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.[12] 1987 saw the entry of EMC Corporation into the SSD market, with drives introduced for the mini-computer market. However, by 1993 EMC had exited the SSD market.[13][14]

Software-based RAM Disks are still used today because they are an order of magnitude faster than the fastest SSD, but they consume CPU resources and cost much more on a per GB basis.[15]

Flash-based SSDs

In 1994, STEC, Inc. bought Cirrus Logic’s flash controller operation, allowing the company to enter the flash memory business for consumer electronic devices.

In 1995, M-Systems introduced flash-based solid-state drives.[16] 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.[17] 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.[18]

In 1999, BiTMICRO made a number of introductions and announcements about flash-based SSDs, including an 18 GB 3.5-inch SSD.[19] 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.[20] At Cebit 2009, OCZ 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.[21] In December 2009, Micron Technology announced the world's first SSD using a 6 gigabits per second (Gbit/s) SATA interface.[22]

Enterprise flash drives

Enterprise flash drives (EFDs) are designed for applications requiring high I/O performance (IOPS), reliability, and energy efficiency. In most cases, an EFD is an SSD with a higher set of specifications, compared to SSDs that would typically be used in notebook computers. The term was first used by EMC in January 2008, to help them identify SSD manufacturers who would provide products meeting these higher standards.[23] 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. Likewise, there may be other SSD manufacturers that meet the EFD requirements without being called EFDs.[24]

Architecture and function

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.[2][25] Other components play a less significant role in the operation of the SSD and vary between manufacturers.

Controller

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.[26] Some of the functions performed by the controller include:[27][28]

The performance of the SSD can scale with the number of parallel NAND flash chips used in the device. A single NAND chip is relatively slow, due to narrow (8/16 bit) asynchronous IO interface, and additional high latency of basic IO operations (typical for SLC NAND, ~25 μs to fetch a 4K page from the array to the IO 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, 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.[29] Micron and Intel initially made faster SSDs by implementing data striping (similar to RAID 0) and interleaving in their architecture. 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.[30] 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.[31] 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.[citation needed]

Memory

Flash memory-based

Most SSD manufacturers use non-volatile NAND flash memory in the construction of their SSDs because of the lower cost compared to DRAM and the ability to retain the data without a constant power supply, 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.[32]

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.[33][34] This can be mitigated or even reversed by the internal design structure of the SSD, such as interleaving, changes to writing algorithms,[34] and higher over-provisioning (more excess capacity) with which the wear-leveling algorithms can work.[35][36][37]

DRAM-based

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. 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. 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).[17][38]

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]

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.[39]

Cache or buffer

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.[29] One SSD controller manufacturer, SandForce, does not use an external DRAM cache on their designs, but still achieve very high performance. Eliminating the external DRAM enables a smaller footprint for the other flash memory components in order to build even smaller SSDs.[40]

Battery or super capacitor

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] 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 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.[28] Most consumer-class SSDs do not have built-in batteries or capacitors;[41] among the exceptions are the Intel 320 series[42] and the more expensive Intel 710 series.[43]

Host interface

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:

Form factor

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, 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.[2]

For general computer use the 2.5" form factor (typically found in laptops) is the most popular. For desktop computers with 3.5" hard disk slots, a simple adapter plate can be used to make such disk fit. Other type of form factors are more common in enterprise applications. A 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).

Standard HDD form factors

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.[2][47] These traditional form factors are known by the size of the rotating media, e.g., 5.25", 3.5", 2.5", 1.8", not by the dimensions of the drive casing.[48]

Box form factors

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]

Bare-board form factors

  • Viking Modular SATA Cube and AMP SATA Bridge multi-layer SSDs
    Viking Modular SATA Cube and AMP SATA Bridge multi-layer SSDs
  • Viking Modular SATADIMM based SSD
    Viking Modular SATADIMM based SSD
  • MO-297 SSD form factor
    MO-297 SSD form factor
  • Custom connector SATA SSD
    Custom connector SATA SSD

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.[49] The SATADIMM from Viking Modular 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. The result is an easy to install SSD with a capacity equal to drives that typically take a full 2.5 in drive bay.[50] At least one manufacturer, InnoDisk, is producing a drive that sits directly on the SATA connector on the motherboard without any other support or mechanical mount.[51] 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[52] or a PCIe-to-SATA bridge device which then connects to SATA flash controller(s).[53]

Ball grid array form factors

In the early 2000s, a few companies introduced SSDs in Ball Grid Array (BGA) form factors, such as M-Systems’ (now SanDisk) DiskOnChip[54] and Silicon Storage Technology’s NANDrive[55][56] (now produced by Greenliant Systems), and Memoright's M1000[57] 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.[58]

Comparison of SSD with hard disk drives

The disassembled components of a hard disk drive (left) and of the PCB and components of a solid-state drive (right)

Making a comparison between SSDs and ordinary (spinning) HDDs is difficult. Traditional HDD benchmarks are focused on finding the performance aspects where they are weak, such as rotational latency time and seek time. As SSDs do not spin, or seek, they may show huge superiority in such tests. However, SSDs have challenges with mixed reads and writes, 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.[59]

Most advantages of solid-state disks over traditional hard drives come from the characteristic of data being accessed completely electronically instead of electro-mechanically. On the other hand, traditional hard drives currently excel by offering much more capacity for the same price.[60]

While SSDs appear to be more reliable than HDDs,[61][62] researchers at the Center for Magnetic Recording Research "are adamant that today's SSDs aren't an order of magnitude more reliable than hard drives".[63] If and when an SSD fails, the failure is likely to be catastrophic, with total data loss. HDDs can fail in this way too, but often give warning that they are failing, allowing much or all of their data to be recovered.[64]

Traditional hard drives store their data in a linear, ordered manner. SSDs, however spend a great amount on rearranging pieces of data and bookkeeping their new locations, the main reason being wear leveling. This puts a big responsibility on the flash memory controller and its firmware to maintain data integrity. One major cause of data loss in current SSDs is firmware bugs, which in HDDs rarely are the source of a problem.[citation needed]

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
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.
Random access time[65] About 0.1 ms - many times faster than HDDs because data is accessed directly from the flash memory Ranges from 5–10 ms due to the need to move the heads and wait for the data to rotate under the read/write head[66]
Read latency time[67] 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).[68] Generally high since the mechanical components require additional time to get aligned
Data transfer rate SSD technology can deliver rather consistent read/write speed, typically ranging from about 100MB/s to 500MB/s, depending on the model. When SSDs access individual smaller blocks, performance is reduced. In general, the speeds are continuously improving.[citation needed] Once the head is positioned, when reading or writing a continuous track, a HDD can transfer data at about 100MB/s. Data transfer rate depends upon rotational speed, which can range from 4,200 to 15,000 rpm.[citation needed]
Consistent read performance[69] Read performance does not change based on where data is stored on an SSD If data from different areas of the platter must be accessed, as with fragmented files, response times will be reduced by the need to seek each fragment
Fragmentation There is no benefit to reading data sequentially (beyond typical FS block sizes), making fragmentation irrelevant for SSDs. Defragmentation would cause wear by making additional writes of the NAND flash cells, which have a limited cycle life.[70][71] Files, particularly large ones, on HDDs usually become fragmented over time if frequently written; periodic defragmentation is required to maintain optimum performance.[72]
Noise (acoustic) SSDs have no moving parts and therefore are silent. HDDs have moving parts (heads, actuator, and spindle motor) and make some sound; noise levels vary between models, but can be significant.
Temperature control[73] 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) can shorten the life of a hard disk, and reliability will be compromised at drive temperatures above 55°C or 131°F. Fan cooling may be required if temperatures would otherwise exceed these values.[74] In practice most hard drives are used without special arrangements for cooling.
Susceptibility to environmental factors[68][75][76] No moving parts, very resistant to shock and vibration Heads floating above rapidly rotating platters are susceptible to shock and vibration
Installation and mounting Not sensitive to orientation, vibration, or shock. Usually no exposed circuitry. May not be specified to operate in all orientations. Must be mounted to protect against vibration and shock. Circuitry may be exposed, and must not contact metal parts. May require dedicated fan.
Susceptibility to magnetic fields [77] No impact on flash memory Magnets or magnetic surges could in principle damage data, although the magnetic platters are usually well-shielded inside a metal case.
Weight and size[75] Solid state drives, essentially semiconductor memory devices mounted on a circuit board, are small and light in weight. HDDs are relatively large and heavy, 3.5" drives more so than 2.5" and 1.8".
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.[78][79][80][81][82] SSDs based on DRAM do not have a limited number of writes. Firmware bugs are currently a common cause for data loss.[citation needed] HDDs have moving parts, and are subject to potential mechanical failures from the resulting wear and tear. Magnetic media also has a limited number of writes, but it is considerably longer than flash memory of little relevance compared to other sources of error.
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, 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.[83] HDDs can overwrite data directly on the drive in any particular sector.
Cost per capacity NAND flash SSDs cost approximately US$0.65 per GB [84] HDDs cost about US$0.05 per GB for 3.5 inch and $0.10 per GB for 2.5 inch drives
Storage capacity In 2011 SSDs were available in sizes up to 2TB, but less costly 64 to 256GB drives were more common. In 2011 HDDs of up to 4TB were available.
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.
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.[29][85][86] 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.[87][88] The lowest-power HDDs (1.8" size) can use as little as 0.35 watts.[89] 2.5" drives typically use 2 to 5 watts. The highest-performance 3.5" drives can use up to about 20 watts.


Comparison of SSD with memory cards

CompactFlash card used as a 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.[90]

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, eventually developing their own unique form factors. The SSD was designed to be installed permanently inside a computer[90]

In contrast, memory cards (Secure Digital (SD), etc.) 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.[90] 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 CF card interface is generally 3-4 times slower than an SSD. As 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 minimum.

Applications

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, the falling prices and increased densities have made it more financially attractive 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. Any company can assess the ROI from adding SSDs to their own applications to best understand if that will be cost effective for them.[2]

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]

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, simply turning the machine off and then on returns it back to its initial virgin 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.

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.[91] A similar technology is available on HighPoint's RocketHybrid PCIe card.[92] 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, allowing 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.[93]

Data recovery and secure deletion

Solid state drives have set new challenges for data recovery companies, as the way of storing data is much more non-linear and complex than of hard disk drives. The strategy the drive operates by internally can largely vary between manufacturers and, the TRIM command zeroes the whole range of a deleted file. Wear leveling also means that the physical and virtual location of data pieces differ.[citation needed]

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.[94]

SSD-optimized file systems

Main article: File systems optimized for flash memory, solid state media

Some computer file systems optimize the use of solid-state drives. Some popular or notable filesystems are listed below.

Good SSD support in a file system requires the implementation of the TRIM command which helps to recycle discarded data, and partition alignment which avoids excessive read-modify-write cycles. Other features such as defragmentation, designed for hard disk drives, are disabled in SSD installations.

Linux systems

The Linux kernel supports the TRIM function starting with version 2.6.33. The ext4 and Btrfs (experimental) file systems are supported when mounted using the discard parameter. Linux distributions usually do not set this kind of configuration automatically during installation.[95] This is because of the notion that the operating system might after all not use the disk optimally when configured as such.[96] The disk utilities take care of proper partition alignment.[97]

Mac OS X

Mac OS X 10.7 (Lion) supports TRIM, as does OS X 10.6.8 Snow Leopard.[98] 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.[99]

Microsoft Windows

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.

Windows 7

Windows 7 has support for SSDs.[100][101] The operating system detects the presence of a SSD and optimizes operation accordingly. For SSD devices Windows 7 disables defragmentation, Superfetch, ReadyBoost, and other[which?] boot-time and application prefetching operations. It 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.[102][103]

Windows Vista

Windows Vista generally expects hard disk drives rather than SSDs.[104][105] 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. This 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 .[106] The proper alignment really does not help the SSD's endurance over the life of the drive, however some Vista operations, 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. 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.[107] Vista does not natively implement TRIM command, either.

ZFS

Solaris as of version 10 Update 6 (released in October 2008), and recent versions of OpenSolaris, Solaris Express Community Edition, Illunos, 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. 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.[108]

FreeBSD

In addition to the ZFS features described above, the Unix File System (UFS) supports the TRIM command.

Swap partitions

On Linux, swap partitions automatically exploit TRIM operations when the underlying drive supports TRIM (no configuration is needed).[109][110] On some operating systems[which?], there might not be a possibility to use the TRIM function on discrete swap partitions. To remedy this issue, swap files inside an ordinary file system may be used.

DragonFly BSD

As a unique feature, DragonFly BSD allows SSD-configured swap to also be used as file system cache.[111] This can be used to boost performance on both desktop and server workloads.

Standardization organizations

The following are noted standardization organizations and bodies that work to create standards for solid-state drives (and other computer storage devices). It also includes organizations who promote the use of solid-state drives. This is not necessarily an exhaustive list.

Organization or Committee Subcommittee of: Purpose
INCITS N/A Coordinates technical standards activity between ANSI in the USA and joint ISO/IEC committees worldwide
T10 INCITS SCSI
T11 INCITS FC
T13 INCITS ATA
JEDEC N/A Develops open standards and publications for the microelectronics industry
JC-64.8 JEDEC Focuses on solid-state drive standards and publications
NVMHCI N/A Provides standard software and hardware programming interfaces for nonvolatile memory subsystems
SATA-IO N/A Provides the industry with guidance and support for implementing the SATA specification
SFF Committee N/A Works on storage industry standards needing attention when not addressed by other standards committees
SNIA N/A Develops and promotes standards, technologies, and educational services in the management of information
SSSI SNIA Fosters the growth and success of solid state storage

Commercialization

Cost and capacity

The technological trend of 50% decline in costs per year is no longer possible in NAND flash due to patents on some key manufacturing processes stifling further competition in the market. Due to this, most current NAND makers anticipate modest cost declines in the period between 2011-2015. Capacities in client SSDs are typically dictated by cost concerns rather than technical limitations of NAND storage.[citation needed].

Availability

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. 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. Either 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.

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. 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.[112] Asus released the Eee PC subnotebook on October 16, 2007, with 2, 4 or 8 gigabytes of flash memory.[113] On January 31, 2008, Apple Inc. released the MacBook Air, a thin laptop with optional 64 GB SSD. The Apple Store cost was $999 more for this option, as compared to that of an 80 GB 4200 RPM hard disk drive.[114] Another option, the Lenovo ThinkPad X300 with a 64 gigabyte SSD, was announced by Lenovo in February 2008.[115] On August 26, 2008, Lenovo released ThinkPad X301 with 128GB SSD option which adds approximately $200 US.

File:Mtron SSD.jpg
The Mtron SSD

In 2008 low end netbooks appeared with SSDs. In 2009 SSDs began to appear in laptops.[112][114]

On January 14, 2008, EMC became the first enterprise storage vendor to ship flash-based SSDs into its product portfolio.[116]

In late 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.[117]

Dell began to offer optional 256 GB solid state drives on select notebook models in January 2009.

In May 2009, Toshiba launched a laptop with a 512 GB SSD.[118][119]

Since October 2010 Apple's MacBook Air line has used a solid state drive as standard.[120]

In December 2010, OCZ RevoDrive X2 PCIe SSD was available in 100GB to 960GB capacities delivering speeds over 740MB/s sequential speeds and random small file writes up to 120,000 IOPS. [121]

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 5.12TB, read speed of 6.0GB/s, write speed of 4.4GB/s and a low latency of 30 microseconds. It has 1.19M Read 512 byte IOPS and 1.18M Write 512 byte IOPS.[122]

In late 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]

At CES 2012, OCZ Technology demonstrated the R4 CloudServ PCIe SSDs capable of reaching transfer speeds of 6.5GB/s and 1.4 million IOPS.[123] Also announced was the Z-Drive R5 which is available in capacities up to 12TB capable of reaching transfer speeds of 16GB/s and 2.52 million IOPS using the PCI Express x16 Gen 3.0[124]

Quality and performance

Main article: Disk drive performance characteristics

SSD technology has been developing rapidly. 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, 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+ hours test run.[125]

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.[126]

See also

References

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External links

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