By David Hill and Jim Handy
Solid state drive (SSD) technology is generally expected to grow in importance in enterprise-class storage as the performance tier of choice. In fact, over time, while tier 1 FibreChannel (FC) and serial-attached SCSI (SAS) drives will not be entirely displaced, tier 0 SSD storage will be used for applications where performance is a paramount objective and tier 2 SATA drives will be used increasingly for applications where price—and not performance—is the primary consideration. That means that the SSD market will bifurcate into a performance tier and a capacity tier that will coordinate with each other.
There is still some question over when this will take place. Would-be users are still trying to figure out how to efficiently optimize SSD. Many others are trying to understand when it makes sense to adopt this new technology. However, the biggest inhibitor to the adoption of SSDs remains cost. On a per gigabyte basis SSDs are much more expensive (about 20X) than hard disk drives (HDDs).
The economic case for SSDs in the enterprise is instead built using a different measure: Price per IOPS. For example, to achieve very high performance in an HDD-based system, data center managers will often use parallelism, spreading data over many spindles, increasing IOPS but resulting in a lot of unused capacity. SSDs are inherently much faster than HDDs, so a single unit with less total capacity can effectively replace numerous lightly utilized drives. This is especially true when "short stroking" is applied reducing usable capacity to less than 20% of an HDD for a relatively small IOPS gain. Usually the single SSD will carry a smaller price tag than the total price of all the HDDs it replaces.
Some argue, nonetheless, that SSD prices are falling so quickly that it is inevitable that they will reach a price-per-gigabyte crossover with enterprise-class HDDs in the near future. This comes from a misperception about how quickly flash memory prices can fall. Although flash SSD prices recently fell faster than HDD prices, such falls are not sustainable. Over the long run SSD gigabyte prices will remain about 20X that of an HDD, so any case based on price per gigabyte will continue to pose a challenge. From this perspective price vs. performance will always be the key justification for the use of SSDs in enterprise data centers. Of course, steep price drops will always temporarily improve the business case for SSDs. This is simply Economics 101 and price elasticity.
SSD vendor Fusion-io believes that it has found a way to significantly reduce the price of enterprise-class flash memory devices without reducing performance or compromising reliability by using what it calls Single-mode Multi-Level Cell (SMLC) technology, which uses multi-level cell (MLC) flash memory technology at the chip level. This compares with standard enterprise-class flash memory which uses single-level cell (SLC). Raw MLC technology is consumer-grade flash memory (which is what you find in removable USB drives) which trades off a much lower cost structure for higher capacity, with as much as 10 times lower endurance than SLC technology.