Whether you're checking market share numbers or SPC-1 performance results, it's clear that solid-state drives (SSDs) are making huge inroads in high-end enterprise storage. As SSDs drop in price and rise in capacity, their superior performance will continue to gradually push spinning disk out of the data center.
But SSDs will ultimately do more than simply replace disk. Recent announcements from EMC and rumors out of Dell's new EqualLogic/Compellent brain trust suggest a transformation of the enterprise storage landscape. To grasp what's afoot, it helps to understand the idea of tiered storage that underlies most storage architectures.
Storage tiering has been around for a while. The idea is to deploy multiple classes of storage hardware that correspond to various points on the performance- versus-capacity spectrum and intelligently allocate data to the most appropriate storage hardware class. For example, you might locate bulk data that will probably see sequential I/O on cheap SATA disk, while transactional database data might live on 15,000-rpm SAS disk.
At first, tiering was almost entirely manual. You'd field two or three different types of disk and, largely through trial and error, shuffle your data around among tiers until the right mix of capacity, cost, and performance was achieved. This was not only time consuming -- requiring very close monitoring of transactional storage demands -- but also not particularly effective, since it was generally done on a volume-by-volume basis rather than block-by-block.
Several storage vendors -- 3Par and EMC are great examples -- saw an opportunity to make everyone's lives easier and introduced automated array-based tiering. This took the onus off the storage administrator and allowed the array to make intelligent decisions about where to locate data based on its usage profile. Thus, individual blocks of a database (perhaps comprising a database index) could be automatically shoveled into fast storage, while less-accessed data stayed on much less expensive, slower storage.