Solid state storage (SSS) is a type of computer storage media that is made from silicon microchips. SSS stores data electronically instead of magnetically, as spinning hard disk drives or magnetic oxide tape do.
Solid-state storage can be found in three form factors: solid state drives (SSD), solid state cards (SSC), solid state modules (SSM). An important advantage of solid-state storage is the fact that it contains no mechanical parts, allowing data transfer to and from storage media to take place at a much higher speed and providing a more predictable lifespan for the storage media.
In addition to providing faster and more consistent input/output (I/O) times, solid-state storage media offers the same levels of data integrity and endurance as other electronic devices and requires less power and cooling than its electromechanical equivalents. It also generally weighs less.
Although solid-state storage technology is not new, interest in how the technology can be used to improve enterprise storage has been relatively recent. Since the turn of this century, processor speeds have continued to increase dramatically while read and write times for mechanical hard disks have not.
Today’s CPUs can process data much faster than hard disk drive storage can supply it. The resulting lag time is known as latency, and one way enterprise administrators have traditionally dealt with high storage latency is by short-stroking the disk drives. Short-stroking is done by deliberately limiting the disk drive capacity so that the disk drive actuator has to move the heads across a smaller number of tracks, reducing seek time. Environments that implement short-stroking typically have to make up for the reduced capacity utilized in each disk drive by increasing the number of disk drives in these configurations. By contrast, SSS devices have zero seek time so their latencies are considerably less, which makes them faster than hard disk drives.
In the enterprise, solid-state storage technology is being used for primary storage but also as cache in front of traditional spinning disks, introducing a new layer between the processor and storage. Some industry experts predict that solid-state storage will eventually replace hard disk storage if silicon factories can meet the increasing demand for product and the price for SSS continues to decline. As of this writing, a 2 terabyte (TB) RAM-based solid-state external storage system would cost approximately six hundred thousand dollars. In contrast, a mechanical hard drive with 2 TB of storage can be purchased for less than $150.
NAND flash is generally used in enterprise SSS products because of its higher capacities and faster erase and write times. It is non-volatile, which means that the data on the storage media remains in memory after the power is turned off. In contrast, RAM-based SSS is volatile; the storage media requires constant power to retain the data it holds. RAM-based systems have the advantage of being relatively insensitive to the number of times data that is written to them.
Flash-based systems have a finite number of writes and like magnetic tape, the media can wear out. Flash-based solid state drives store data in single-level (SLC) or multi-level (MLC ) flash memory cells that are grouped into pages and pages are organized into blocks. Read and write operations are page-oriented. Erase operations apply only to entire blocks. Disk drives and adapter cards can be either RAM or flash-based, but USB drives are almost always flash-based.