Storage Analyst Jim Handy says “NAND Cache is Back!”

Storage analyst and Grand Poobah Jim Handy has just released a free White Paper titled “NAND Cache is Back: SSD Performance at an HDD Price” and it’s worth a look if you are interested in either the market for NAND Flash or have any interest in PC and server storage. The reason this White Paper is worth a look is because Handy goes into substantial quantitative detail with extensive graphs in his analysis and mapping of the intersection between NAND Flash memory and HDD storage. SSDs aren’t taking the consumer- and client-class PC world by storm, as Handy’s plots demonstrate, because large amounts of storage based on NAND Flash continues to cost about 20x per Gbyte more than HDD storage. For that price differential, most people strongly prefer high-capacity HDDs over SSDs. In fact, writes Handy, SSD penetration into PC sales is still less than 1%. However, NAND Flash caches combined with HDD storage can achieve near-SSD performance and HDD capacities at substantially lower cost than can SSDs, and Handy forecasts a bright future for such caches.

Using NAND Flash to boost HDD performance in PCs isn’t new. Handy’s White Paper ticks off prior attempts including Intel’s Robson/Turbo Memory and Braidwood and Microsoft’s ReadyBoost. He cites two reasons these technologies didn’t become part of mainstream PC hardware. The first reason was that some of these attempts used an inadequate amount of NAND Flash memory. A cache needs to be larger than the next memory in the hierarchy--RAM in this case--or the cache will not be effective and the resulting performance gain will be unimpressive. The other issue, he writes, is that the support software wasn’t quite there.

Handy’s White Paper then delves into the real cost of NAND Flash memory, from which he derives a fascinating model of how much NAND Flash cache PC users might feel they can afford. His conclusion is that the cost of the NAND cache must fall somewhere between 20% and 200% of the cost of the PC’s HDD. Based on the consistent, longstanding 20x price difference between NAND Flash and HDD storage, that 20x price differential translates into a NAND Flash capacity of anywhere between 4% and 40% of the associated HDD’s capacity. Although that’s Handy’s bottom line in this White Paper, I think you’ll really find it worthwhile to download and read the full White Paper to see how Handy arrives at this conclusion. This part of Handy’s White Paper addresses the issue of NAND Flash cache size from the perspectives of cost and effectiveness. The rest of the White Paper addresses the issue of support software. This latter part of the White Paper discusses Denali’s Dataplex storage-management software and its performance based on the SYSmark performance numbers. Handy concludes this section by writing “a low-cost NAND cache is significantly more likely to penetrate the PC than an expensive SSD, especially if it can yield 80% or more of the performance of an SSD for only a fraction of the added cost.”

The final part of Handy’s White Paper then analyzes the effect NAND Flash caches will have on the overall NAND Flash market if Flash caches successfully penetrate the PC arena. Handy has a pretty surprising conclusion and I’m not going to preempt his White Paper by disclosing the conclusion here. Go get the White Paper and see for yourself. It’s free and available on Handy’s Web site at http://www.objective-analysis.com/. Scroll down to the well-camouflaged “White Papers” section on the home page and click on the line that reads “Denali's Dataplex, NAND Cache is Back! Click HERE.”