L O S T C I R C U I T S

Enter Solid State Drive Technology

About 2 years ago, the storage landscape changed abruptly. The new hot storage media pushing into the market is NAND flash memory, one of the two major forms of flash memory named after its similarity to a NAND logical gate. NAND flash memory-based drives have been around for almost a decade pioneered by SimpleTech (founded by the Moshayedi brothers and later acquired by STEC because of its flash technology) however, until recently, larger capacity drives were cost prohibitive. However, NAND flash production has been ramped up dramatically over the past years, with essentially every foundry betting their life on its proliferation and profitability. To put things in to perspective, in 2008, NAND flash production for the first time exceeded DRAM production with respect to total number of bits manufactured, in 2009, total number of NAND flash bits manufactured will exceed total number of memory bits ever manufactured since the beginning of time – or the digital age, whichever came first.

One of the biggest - yet always overlooked - changes in the storage market coming with the introduction of NAND flash memory based solid state drives (SSDs) is that it really doesn’t take very much to become a manufacturer now. What is needed is a controller, some firmware, a printed circuit board and a boatload of flash memory plus a flow solder station to assemble the whole unit. This is one of the incentives that has attracted quite a few bigger and smaller players into this emerging market with a projected growth rate of some 1000% annually. In a perfect world, this concept would work, reality, however, often bites.

Steffen Helmold, ex SimpleTech, then Seagate and now at Sandforce summarized the gist of Solid state drives at a recent JEDEC Flash summit: “When we eliminated the mechanical parts of hard disc drives and moved to solid state memory drives we thought we had solved all problems, only to find that we opened a whole new can of worms”. In other words, what appeared simple at the surface turned out a major obstacle course with respect to bringing SSDs to a reliable and reproducible level of performance and data retention.

As a primer for the following, we mention two major issues with SSDs:

• 1) HDDs can be put into storage for a decade and then, provided that there are still systems out there that support the interface, they can be plugged in and the data will be readily accessible. NAND flash-based SSDs will lose their data over time, even if they are powered down and in storage.
• 2) HDDs will show some degradation of performance over time, primarily relating to filling up of the outer diameter tracks and fragmentation of the drives’ media but a defragmentation will restore the performance since it is defined by spindle speed and media area density and those parameters never change. SSDs will show some initial extreme performance but degrade rapidly after heavy usage.

Some of the above issues can be prevented or at least ameliorated but in order to devise the proper strategies, it is of utmost importance to understand some of the fundamentals of the technology.