solid-state storage

Contributor(s): Brien Posey

Solid-state storage (SSS) is a type of computer storage media made from silicon microchips. SSS stores data electronically instead of magnetically, as spinning hard disk drives (HDDs) or magnetic oxide tape do.

Solid-state storage can be found in three form factors: solid-state drives (SSD), solid-state cards (SSC) and solid-state modules (SSM). An important advantage of solid-state storage is 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. Because there are no moving parts, SSDs produce far less heat than HDDs.

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.

Solid-state storage terminology

Solid-state storage trends

Although solid-state storage technology is not new, interest in how the technology can be used to improve enterprise storage has been relatively recent. Part of this trend can be attributed to reductions in price, but hardware performance also plays a role. Since the turn of this century, processor speeds have continued to increase dramatically while read and write times for mechanical HDDs have not.

Today’s CPUs can process data much faster than HDD 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 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 used in each disk drive by increasing the number of disk drives in these configurations. In contrast, solid-state storage devices have zero seek time. This considerably reduces their latencies, which makes them faster than HDDs, especially for random read/write operations. SSS devices have less of a performance advantage when it comes to sequential read/write operations.

In the enterprise, solid-state storage technology is used for primary storage and also as cache in front of traditional spinning disks, introducing a new layer between the processor and storage. Some industry experts predict 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.

Cost of solid-state storage

Not that long ago, a 2 terabyte (TB) RAM-based solid-state external storage system would cost approximately $600,000. Today, a 2 TB RAID 0 PCI Express-based SSD can be purchased for as low as $800. A 1 TB SSD can be purchased for about $300. While SSD prices have decreased dramatically, SSDs are still more expensive than HDDs. A mechanical HDD with 2 TB of storage can be purchased for less than $150.

Types of solid-state storage systems

There are two types of solid-state systems: flash memory-based systems and RAM-based systems. There are also two types of flash memory: NAND flash and NOR flash.

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 the data on the storage media remains in memory after the power is turned off. In contrast, RAM-based solid-state storage 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 is written to them.

Flash-based systems have a finite number of writes and, like magnetic tape, the media can wear out. Flash-based SSDs store data in single-level cell (SLC) or multi-level cell (MLC) flash memory cells grouped into pages, and pages organized into blocks. Read and write operations are page-oriented. Erase operations apply only to entire blocks. Disk drives and adapter cards can be RAM- or flash-based, but USB drives are almost always flash-based.

This video (at left) with Demartek LLC founder and president Dennis Martin delves into solid-state storage technology best practices and developments surrounding the technology.

This was last updated in May 2015

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Do you think solid-state storage technology will ever be priced competitively with hard disk drives?

Of course, it all depends on how you measure things. If you just look at $/GB, flash storage will continue to be more expensive than spinning disk, although the delta has narrowed considerably in the last few years. But if you look at what might be a more practical parameter--$/IOPS--the price of flash approaches (or betters) that of hard drives. And toss in compression and dedupe, which flash handles more efficiently, and you could easily make the argument that there is price parity between flash and HDDs today. 


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