solid state drive (SSD) RAID

Solid state disk RAID (redundant array of independent disks) is a strategy for improving performance that involves dividing and storing the same data on multiple solid state drives (SSDs).

Solid-state drive RAID is a strategy for improving performance that involves dividing and storing the same data on multiple solid state drives (SSDs).

A group of solid-state drives (SSDs) are connected together in the same fashion as has been done in the past with mechanical hard disk drives (HDDs) to create a redundant array of independent disks (RAID). An operating system (OS) sees the RAID as one large disk, but because read and write operations are being spread out over multiple disks, inputs/outputs (I/Os) can be carried out simultaneously, thereby speeding up performance.

A redundant array of SSDs offers reduced risk of data loss, greater throughput, and enhanced fault tolerance compared with a single SSD. The lack of moving parts translates to reduced access time, lower operating temperature, and superior I/O performance compared with mechanical HDDs. However, ideal SSD RAID performance requires the optimum combination of microprocessor, cache, software and hardware resources. When all these factors work together in the best possible way, an SSD RAID can significantly outperform a RAID of comparable storage capacity that comprises HDDs. Failure to properly dovetail the underlying technologies can result in performance that does not exceed, and may actually fall behind, mechanical HDDs.

In the best-case scenario, an SSD RAID can yield I/O performance upwards of 100 times better than a comparable array constructed from mechanical drives. These results were obtained by Samsung when comparing an SSD to an HDD operating at 15,000 revolutions per minute (rpm). More commonly, the I/O performance of an array of SSDs can be expected to exceed that of a comparable HDD array by a factor of at least 10.

A typical SSD consumes around two watts (2 W) of power, while a comparable hard drive requires about 10 W. When large numbers of drives are combined, the power savings of an SSD RAID compared with a mechanical RAID can translate to significantly lower long-term operating cost. In large data centers, the improved efficiency of SSDs compared with mechanical drives can also reduce the cooling cost, both in terms of simpler cooling systems and lower electric bills.

SSD RAIDs have limitations and drawbacks, as does any emerging technology. Most notable is the higher price per gigabyte compared with HDD arrays of comparable storage capacity. Solid-state storage devices can only execute a certain number of write cycles before they become unreliable and must be replaced. Although the best SSDs have life expectancies comparable to mechanical HDDs, the replacement cost for an SSD exceeds the replacement cost for an HDD of comparable storage capacity.

This was first published in January 2012

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