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Solid-state drive 

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This article refers to both flash and DRAM-based solid-state drives. For other flash-based solid-state storage, see flash drive and USB flash drive.
An SSD in standard 2.5-inch (64 mm) form-factor.
An SSD in standard 2.5-inch (64 mm) form-factor.
DDR SDRAM based SSD
DDR SDRAM based SSD

A solid-state drive (SSD) is a data storage device that uses solid-state memory to store persistent data. Unlike flash-based memory cards, a SSD emulates a hard disk drive, thus easily replacing it in most applications. An SSD using SRAM or DRAM (instead of flash memory) is often called a RAM-drive.

The original usage of the term solid-state (from solid-state physics) refers to the use of semiconductor devices rather than electron tubes, but has in this context been adopted to distinguish solid-state electronics from electromechanical devices as well. With no moving parts, solid-state drives are inherently less fragile than harddisks and therefore also silent (unless a cooling fan is used); as there are no mechanical delays, they usually enjoy low access time and latency.

SSDs have begun to appear in laptops,[1][2] although they are at present substantially more expensive per unit of capacity than hard drives.

Contents

History

 Please help improve this article or section by expanding it. Further information might be found on the talk page or at requests for expansion. (February 2007)

First ferrite memory SDD devices (auxiliary memory units, as they were called at the time) emerged in the era of tube computers.citation needed But with the introduction of drum storage units their use was discontinued as extremely expensive. Later (in 1970th-1980th ) the idea was implemented in semiconductor memory for the early supercomputers of IBM, Amdahl and Cray[3], but again the high price made them built-to-order and quite seldom used product.

In 1978 StorageTek developed the first modern type of solid-state drive. In the mid-1980s Santa Clara Systems introduced BatRam, an array of 1 megabit DIP RAM Chips and a custom controller card that emulated a hard disk. The package included a rechargeable battery to preserve the memory chip contents when the array was not powered. The Sharp PC-5000, introduced in 1983, used 128 kilobyte (128 KiB) solid-state storage cartridges, containing bubble memory.

RAM "disks" were popular as boot media in the 1980s when hard drives were expensive, floppy drives were slow, and a few systems, such as the Amiga series, the Apple IIgs, and later the Macintosh Portable, supported such booting. At the cost of some main memory, the system could be soft-rebooted and be back in the operating system in mere seconds instead of minutes. Some systems were battery-backed so contents could persist when the system was shut down.

In 1995 M-Systems introduced flash-based solid-state drives. (SanDisk acquired M-Systems in November 2006). Since then, SSDs have been used successfully as hard disk drive replacements by the military and aerospace industries, as well as 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.

The Gigabyte i-RAM uses standard DDR modules and connects to its host via Serial ATA. This card can use the system's standby power (also used for Wake-on-LAN and similar features) to maintain its RAM contents even with the system powered off, and includes a battery that can retain the data when the system is completely disconnected from power.

In 2008, a new class solid state-based storage devices was introduced: Enterprise Flash Drives (EFDs).citation needed EFDs are designed specifically for use in enterprise and data center environments requiring high levels of IOPS (Input/Output Operations Per Second) performance, reliability and energy efficiency. EFDs were originally introduced by EMC Corporation in January 2008 with the announcement of the company’s Symmetrix DMX-4 arrays.[4]

Architecture and function

An SSD is commonly composed of either DRAM volatile memory or NAND flash non-volatile memory.

Flash based

Most SSD manufacturers use non-volatile flash memory to create more rugged and compact devices for the consumer market. These flash memory-based SSDs, also known as flash drives, do not require batteries. They are often packaged in standard disk drive form factors (1.8-inch, 2.5-inch, and 3.5-inch). In addition, non-volatility allows flash SSDs to retain memory even during sudden power outages, ensuring data retrievability. Though flash SSDs are significantly slower than DRAM (and even traditional HDDs on big files), they usually perform better than traditional hard drives (at least with regard to reads) because of negligible seek time (flash SSDs have no moving parts, thus eliminating spin-up time, and greatly reducing seek time, latency and other delays inherent in conventional electro-mechanical disks).

DRAM based

SSDs based on volatile memory such as DRAM are characterized by ultra fast data access, generally less than 0.01 milliseconds (over 250 times faster than the fastest hard drives in 2008), and are used primarily to accelerate applications that would otherwise be held back by the latency of Flash SDDs or traditional HDDs. DRAM-based SSDs usually incorporate internal battery and backup storage systems to ensure data persistence. Some RAM SSD have built-in UPS. If power is lost for any reason, the battery keeps the unit powered for sufficient time to allow the copying of all data from random access memory (RAM) to the back-up storage or to allow transfer to another computer. Then, when the power is restored, data is copied back to RAM from the back-up storage, and the SSD resumes normal operation. (This is not unlike the hibernate function used in modern operating systems, which saves the entire contents of memory to nonvolatile storage before power-down, to be rewritten into memory upon power-up.)

A secondary computer with a fast network connection can be used as a RAM based SSD.[5]

Open casing of 2.5” traditional hard disk drive (left) and solid-state drive (center).
Open casing of 2.5” traditional hard disk drive (left) and solid-state drive (center).

DRAM based solid-state drives are especially useful on computers that already have the maximum amount of supported RAM. For example, some computer systems built on the x86-32 architecture can effectively be extended beyond the 4 GB limit by putting the paging file or swap file on an SSD. Owing to the bandwidth bottleneck of the bus they connect to, DRAM SSDs cannot read and write data as fast as main RAM can, but they are far faster than any mechanical hard drive. Placing the swap/scratch files on RAM SSD, as opposed to a traditional hard drive, can therefore provide a significant performance increase.

DRAM-based SSDs may also work as a buffer cache mechanism. Whenever data is written to memory, the corresponding block in memory is marked as dirty, and all dirty blocks can be flushed to the actual hard drive based on the following two criteria:

  1. Time (e.g. every 10 seconds, flush all dirty data);
  2. Threshold (when the ratio of dirty data to SSD size exceeds some predetermined value, flush the dirty data).

Comparison with hard disk drives

A comparison (with benchmarks) of SSDs, Secure Digital High Capacity (SDHC) drives, and hard disk drives (HDDs) is given in the reference.[6]

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

Advantages

  • Faster start-up – as no spin-up is required. (RAM & Flash)
  • Typically fast random access for reading – as there is no read/write head to move. (RAM & Flash)
  • Extremely low read latency times – as SSD seek-times are orders of magnitude lower than the best current hard disk drives.[7] (RAM) In applications where hard disk seeks are the limiting factor this results in faster boot and application launch times ( see Amdahl's law).[8] (RAM)
  • Extremely fast write (RAM only)
  • No noise: a lack of moving parts makes SSDs completely silent, unless, as in the case of some high-end and high-capacity models, they have cooling fans attached. (RAM & Flash)
  • For low-capacity flash SSDs, low power consumption and heat production when in active use - although high-end SSDs and DRAM-based SSDs may have significantly higher power requirements. (Flash)
  • High mechanical reliability – the lack of moving parts almost eliminates the risk of mechanical failure. (RAM & Flash)
    • Ability to endure extreme shock, high altitude, vibration and extremes of temperature: once again because there are no moving parts.[9] This makes SSDs useful for laptops, mobile computers, and devices that operate in extreme conditions. (Flash)[8]
  • Larger range of operating temperatures. Typical hard drives have an operating range of 5-55 degrees C. Most flash drives can operate at 70 degrees, and some industrial grade drives can operate over an even larger temperature range.[10]
  • Relatively deterministic read performance:[11] unlike hard disk drives, performance of SSDs is almost constant and deterministic across the entire storage. This is because the seek time is almost constant and is not dependent on the physical location of the data, and so, file fragmentation has almost no impact on read performance.
  • For low-capacity SSDs, lower weight and size: although size and weight per unit storage are still better for traditional hard drives, and microdrives allow up to 20 GB storage in a CompactFlash 42.8×36.4×5 mm (1.7×1.4×.2 in) form-factor. Up to 256 GB, SSDs are currently lighter than hard drives of the same capacity.[9]

Disadvantages

  • Price – as of mid-2008, SSD prices are still considerably more costly per gigabyte than are comparable conventional hard drives: around USD 3.50 per GB[12] for flash drives and over USD 80 per GB for RAM-based compared to typically less than USD 0.26 (Retail) and as low as 0.14 for OEM models for mechanical drives.
  • Capacity – although currently far lower than that of conventional hard drives, SSD capacity is predicted to increase rapidly, with experimental drives of up to 1 TB in test.[13][14]
  • Higher vulnerability to certain types of effects, including abrupt power loss (especially DRAM based SSDs), magnetic fields and electric/static charges, in comparison to normal HDDs (which store the data inside a Faraday cage).dubious – discuss
  • Limited write cycles – flash-memory cells will often wear out after 10,000-100,000 write cyclescitation needed, while high endurance cells may have an endurance of 1–5 million write cycles (many log files, file allocation tables, and other commonly used parts of the file system exceed this over the lifetime of a computer.[15] Special file systems or firmware designs can mitigate this problem by spreading writes over the entire device (so-called wear levelling), rather than rewriting files in place.[16] Today's drives can last up to 20 years with average usage.dubious – discuss An example for the lifetime of SSD is explained in detail in this wiki.dubious – discuss SSDs based on DRAM, however, do not suffer from this problem.
  • Slower write speeds – as erase blocks on flash-based SSDs generally are quite large, they are far slower than conventional disks for random writes and therefore vulnerable to write fragmentation,[17] and in some cases for sequential writes.[8] SSDs based on DRAM do not suffer from this problem.
  • Lower storage density – hard disks can store more data per unit volume than DRAM or flash SSDs, except for very low capacity/small devices.
  • Higher power consumption at idle or under low workloads laptop battery runtimes decrease when using an SSD over a 7200 RPM 2.5" laptop hard drive,[18] flash drives also take more power per gigabyte.
    • RAM based SSD require more power than hard disks, both operating and when turned off.[19]

Commercialization

Cost and capacity

Until recently, solid-state drives were too costly for mobile computing. As flash manufacturers transition from NOR flash to single-level cell (SLC) NAND flash and most recently to multi-level cell (MLC) NAND flash to maximize silicon die usage and reduce associated costs, "solid-state disks" are now being more accurately renamed "solid-state drives" – they have no disks but function as drives – for mobile computing in the enterprise and consumer electronics space. This technological trend is accompanied by an annual 50% decline in raw flash material costs, while capacities continue to double at the same rate. As a result, flash-based solid-state drives are becoming increasingly popular in markets such as notebook PCs and sub-notebooks for enterprises, Ultra-Mobile PCs (UMPC), and Tablet PCs for the healthcare and consumer electronics sectors. Major PC companies have now started to offer such technology. The capacity of these drives varies from 12 GB to 256 GB.

Availability

Even though solid-state drive (SSD) technology has been marketed to the military and niche industrial markets since the mid-1990s, it is only recently that the enterprise sector has taken notice of the benefits that SSDs can offer, as key SSD technologies emerge, prices drop and new case studies, along with analyst reports, are published.

CompactFlash card used as SSD
CompactFlash card used as SSD

Along with the emerging enterprise market, SSDs have been appearing in ultra-mobile PCs and a few lightweight laptop systems, adding a US$ $600 to $1000 premium to the price of a HDD-equipped laptop, depending on the capacity, form factor and transfer speeds. Only a handful of companies offer large (128 GB or larger) SSD drives with write speeds adequate for replacing traditional drives, and these drives are available in limited quantities and are very expensive. Already some manufacturers have begun shipping affordable, fast, energy-efficient drives priced at $350 to computer manufacturers. For low-end applications, a USB memory stick may be used as a Flash hard drive for $10 to $100 or so, depending on capacity, or 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 not 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 megabytes per second while the more expensive upmarket cards claim speeds of up to 40 MB/s.

One of the first mainstream releases of SSD was the XO Laptop built under the 'One Laptop Per Child' project. Mass production of these computers built for children in developing countries begun in December 2007. These machines use 1024 MiB SLC NAND flash as primary storage solution which is considered more suitable for the harsher than normal conditions they are expected to be used in. Dell has begun shipping ultra-portable laptops with SanDisk SSDs on April 26, 2007.[1] Asus released the Eee PC subnotebook on October 16 2007, and after a successful commercial start in 2007, expects to ship several million PCs in 2008, with 2, 4 or 8 gigabytes of flash memory.[20] On January 31, 2008 Apple Inc. released the MacBook Air, a thin laptop with optional 64 GB SSD. The cost is $599 more for this option if configured in the Apple Store, as compared to that of an 80 GB 4200 rpm Hard Disk Drive.[2] Another option - IBM Lenovo ThinkPad X300 with a 64Gbyte SSD - was announced by Lenovo in February 2008,[21] and is currently available to consumers in some countries.

On July 15, 2008, Advanced Media, Inc. /RiTEK USA first announced high performance / low cost MLC SSD -RiDATA Ultra-S Plus MLC series SSD. Capacity includes 32 GB, 64 GB, and 128GB. Prices were $169 for 32 GB, $257 for 64 GB and $475 for 128 GB.

Product Timeline

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The Mtron SSD
The Mtron SSD
  • Mtron announces flash memory solid-state drive, performing 100 MB/s Read, 80 MB/s Write, 72,000 Max IOPS in December 2005.[22]
  • SanDisk released a 32 GB 2.5-inch (64 mm) solid-state drive on March 13, 2007. The SSD SATA 5000 is being sold to computer manufacturers for $350.
  • Hyperdrive release the rev.4 designed to use 8 standard DDR ECC Registered memory modules on a native SATA and IDE interface. February 2007.[25]
  • On February 26, 2007, SMART Modular Technologies launched its first line of XceedUltra solid-state drives (SSDs). SMART's XceedUltra U100 is the industry's first SSD with a serial ATA (SATA) interface that achieves sustained read speeds of 100 MB/s and write speeds of 60 MB/s.
  • STEC, Inc. has announced a 64 GB SSD. On April 18, 2007, STEC announced 256 GB enterprise-level drives available immediately, and 512 GB drives available late 2007.[27][28]
  • Lexar ExpressCard SSD is shipping in 4 GB, 8 GB, and 16 GB capacities, as of May 2007.[29]
  • PNY announces SSD lineup targeting OEM customers in 1.8" and 2.5" form-factors, PATA and SATA, capacities reaching 128 GB in May 24, 2007.[30]
  • Power Quotient International (PQI) Announces 256 GB SSD on 28 May 2007.[31]
  • SanDisk announces 64 GB SSDs of 1.8 UATA 5000 and 2.5 SATA 5000 on June 4, 2007.[32]
  • Violin Memory announces 1010 memory appliance on August 2, 2007. The DRAM version of their appliance is capable of supporting 504 GB of memory and the expected flash version will scale to a little over 5 TB. This 2U appliance is capable of over 3 Million random I/O per Second (IOPS). It is attached to a server through a 20 Gbit/s PCI Express connection (8 lanes) and has demonstrated 1400 MB/s read rate and 1000 MB/s write rate with 3μs latency.[33]
  • SMART On August 7, 2007, SMART Modular Technologies launched the XceedLite SATA SSD product line.
  • Fusion-io announces ioDrive PCIe x4 NAND Flash Card 640 GB 100,000 IOPS 800 MB/s on September 24, 2007.[34]
  • Trident Space & Defense in October 2007 introduces rugged drives (shock, vibration, splash resistant) for military and industrial applications in a standard 2.5-inch (64 mm) form factor with 9.4 mm height.
  • BiTMICRO launches SSD 3.5" with a capacity of 1.6 TB in November 2007.[35] Will mostly be used for the army.
  • SanDisk released a 32 GB 1.8-inch (46 mm) solid-state drive on January 4, 2008.
  • Texas Memory Systems achieved the highest number of IOPS (291,208.58) and the lowest Price Performance ($0.67/IOPS) when they took part in the Storage Performance Council's SPC-1 IOPS test in January 2008.[36]
  • Imation announces Pro7000 SSD drive with 120 MB/s read and 90MB/s write performance [IOPS:81000/18000] and 0,1ms avg access time on March 10, 2008.[37]
  • ROMEDIA announced a 3.5-inch 128 GB solid-state drive on stock for sale on March 2008.[38]
  • Memoright announces SSD drives with 115 MB/s read and write performance confirmed on May 9, 2008.[39]
  • Samsung announces increase in capacity of its flash-based SSD line to 256 GB on May 25, 2008. This drive has reported speeds of 200MB/sec read and 160MB/sec write.[40]
  • Toshiba introduced a notebook that the vendor claims is the lightest laptop (2.4-pound) with a 128-GB Solid-State Drive, June 17, 2008.[41]
  • Fusion-io and Hewlett Packard announce working together to adapt the ioDrive flash SSD to provide acceleration in HP's BladeSystem and Enterprise Servers.June 18, 2008.[42]
  • On July 15, 2008, Advanced Media, Inc. / RITEK USA announced the world fastest MLC SSD. Ultr-S Plus SSD with 32GB, 64GB and 128GB. Read speed is up to 152MB/s based on Datamarck testing result, an independent site measuring performance of storage devices.[43] Compared to traditional hard drive, SSD is about 50%+ faster.
  • On August 5, 2008 MICRON introduced world fastest SSD with read/write speed of up to 250MB/s. [44]
  • On August 12, 2008 Fusion-io Introduced it's new “Flashback” Protection technology which is a protective chip level RAID technology for guaranteeing NAND array reliability on a single Enterprise Flash Drive.[45]

See also

References

  1. ^ a b Aughton, Simon (2007-04-25). "Dell Gets Flash With SSD Option for Laptops". IT PRO.
  2. ^ a b Macbook Air Specifications
  3. ^ [1]
  4. ^ Mellor, Chris (2008-01-14). "EMC has changed enterprise disk storage for ever". Techworld.com.
  5. ^ RIndMA Disk
  6. ^ Jackson, Jerry (2008-02-17). "SDHC Cards vs Hard Drive vs SSD". NotebookReview.com, TechTarget.
  7. ^ Radding, Alan. "Solid-state storage finds its niche". StorageSearch.com. Retrieved on 2007-12-29. Registration required.
  8. ^ a b c Meyev, Aleksey (2008 -04-23). "SSD, i-RAM and Traditional Hard Disk Drives". X-bit labs.
  9. ^ a b "SSD vs HDD". SAMSUNG Semiconductor.
  10. ^ "Memoright SSDs: The End of Hard Drives?". Retrieved on 5 August 2008.
  11. ^ AnandTech: Super Talent SSD: 16GB of Solid State Goodness
  12. ^ Shah, Agam (2008-05-30). "Seagate plans SSD, 2 TB hard drive for next year". Computerworld. Retrieved on 2008-05-30.
  13. ^ "Imperial Technology Announces One Terabyte SSD". Imperial Technology Inc.
  14. ^ Solid Data Systems, Inc. (2007-07-17). "SDS Offers 1TB SSD". Press release.
  15. ^ Kerekes, Zsolt. "SSD Myths and Legends - "write endurance"". StorageSearch.com.
  16. ^ Corbet, Jonathon (2007-05-15). "LogFS". Linux Weekly News.
  17. ^ Dumitru, Douglas (2007-08-16). "Understanding Flash SSD Performance". EasyCo LLC.
  18. ^ "Flash SSD Update: More Results, Answers : An Apology First – And One New SSD To Prove Us Right". Tom's Hardware (2008-07-14). Retrieved on 2008-07-24.
  19. ^ Schmid, Patrick (2007-11-07). "HyperDrive 4 Redefines Solid State Storage : HyperDrive 4 - The Fastest Hard Disk In The World?". Tom's Hardware.
  20. ^ Chen, Shu-Ching Jean (2007-06-07). "$199 Laptop Is No Child's Play", Forbes. Retrieved on 2007-06-28. 
  21. ^ Lenovo (2008-02-26). "Road Warriors Get Ready – Lenovo Delivers "No Compromises" Ultraportable ThinkPad X300 Notebook PC". Press release.
  22. ^ MTRON | Home
  23. ^ Future of Flash revealed
  24. ^ A-DATA exposes 128GB SSD to the camera
  25. ^ HyperOs Systems - Hardware
  26. ^ Super Talent readies 128 GB flash drive, 4 GB DIMMs
  27. ^ SimpleTech announces "world's thinnest" 2.5-inch 64GB SSD
  28. ^ SimpleTech announces 512GB and 256GB 3.5-inch SSD drives
  29. ^ Lexar - Newsroom - Press Releases
  30. ^ PNY
  31. ^ As The Forefather of Industrial SSDs, PQI Sets New Standards with New High Speed and Large Capacity Industrial CF and SSD
  32. ^ SanDisk Launches 64 Gigabyte Solid State Drives for Notebook PCs, Meeting Needs for Higher Capacity
  33. ^ Violin 1010 released
  34. ^ Fusion-io announces the next generation of enterprise storage
  35. ^ bitmicro.com
  36. ^ storageperformance
  37. ^ Imation - Solid State Drives
  38. ^ Dutch distributor sells from stock
  39. ^ tomshardware.com
  40. ^ Samsung announces crazy fast 256GB SSD, our knees buckle - Engadget
  41. ^ Toshiba Offers Lightest (2.4-pound) Notebook With 128-GB Solid-State Drive
  42. ^ HP adding solid-state memory to its servers
  43. ^ datamarck - benchmarks
  44. ^ Micron Introduces Next-Generation RealSSD™ Solid State Drives For Enterprise Server And Notebook Applications
  45. ^ [2]

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