SSD endurance is an important concern that stands in the way of SSD adoption in a number of data centers. Since flash is new to the enterprise (and computing systems are a new market for flash) important issues including wear specifications still need to be hammered out.
Until flash SSDs started experiencing adoption in standard computing environments, nobody really anticipated the difficulties that would arise from flash’s inherent wear-out mechanism. Most flash manufacturers erroneously believed that the only writes to disk occurred when files were saved or programs were installed. We have heard that certain PATA SSDs even shipped without any wear leveling, a rumor that may or may not be true, but certainly one that would result in an extraordinarily brief lifetime in any environment based on a standard operating system. Meanwhile, software was not configured with flash in mind, and newer operating systems incorporated automatic defragmentation, a feature that provided no benefit to a flash-based SSD but shortened its useful life through unnecessary wear.
SSD wear concerns are now being addressed by standards bodies, and a discussion of this appears in an EE Times article titled “How to know if your SSD will go the distance,” by Teresa Worth of Seagate. In the article Worth explains
In September 2010, the JEDEC Solid State Association published two sets of standards for SSD endurance and reliability. JESD218A defines endurance verification requirements for both client and enterprise SSDs. JESD219 defines workload endurance requirements for enterprise SSDs only.
The article gives the JEDEC definitions of requirements for two classes of SSD, enterprise and client, then goes on to explain why wear exists, and how MLC and SLC wear differs. It’s worth a read.
Over time SSDs will be well defined and even better understood, and we will be able to look back in wonder at the difficulties of bringing this technology to enterprise reliability levels. Thanks to the important work these standards bodies are doing that we will soon reach a point where SSD wear will be consistently specified and users will adopt SSDs based upon an understanding of their behavior, instead of postponing adoption due to worries of potentially undocumented time bombs.