When should I use SSD instead of SAS or SATA?

The criteria for deploying solid state drives (SSDs) are no different to choosing any other type of disk technology. You should always base your choice around three primary factors: price, performance and capacity.

Three key features

The cost of SDDs is approximately 10 times higher than that of SAS, which is in turn greater than SATA. The sustainable IO performance of SSDs can, however, be 40-60 times greater than that that of SAS and SATA, respectively. The standard capacity of SSDs has also increased to 600GB, but this is still rather low in comparison to SAS (900GB) and SATA (3TB).

Business needs

SSDs are therefore of particular interest when an application's performance requirements outweigh those of cost and capacity, being especially well suited for applications - often the most business critical - with the highest random read and write requirements. In some cases, organisations have dramatically reduced datacentre footprint and storage costs, not to mention power and cooling needs, simply by replacing hundreds of SAS drives with a much smaller number of strategically placed SSDs.

Tiered storage

SSDs should therefore be an important consideration for any organisation's tiered storage strategy, although in order to extract the greatest value from them, it is important that they are deployed in conjunction with the vendor's thin provisioning and automated-tiering products. Thin provisioning can greatly improve the utilisation of the SSD capacity, and avoid costly 'white space' as only actual data is written to the drives.

Automated tiering promotes data that requires the greatest performance to SSD, and relegates less demanding data to SAS or SATA. This use of different drive technologies together with thin provisioning and automated tiering maximises the effective use and capacity of SSDs without the need for operator intervention.

David Boyle is a senior consultant at GlassHouse Technologies.