This month, we take a look at an idea that I hadn’t heard before from PMC-Sierra on how SSDs are really more power- and cost-effective in a very high transactional environment.
Reshaping the direction of Embedded Computing Design this year has proven interesting for me because we’re starting to hear stories from folks we haven’t heard from with ideas we hadn’t considered. The folks at PMC-Sierra recently briefed me on a new product launch that felt like an enterprise story at first but turns out to be very much an embedded story. I’d like to share and see if you agree.
] architecture driving eight SATA/SAS ports at 6 GBps each from a PCI Express host.
Cameron used the diagram depicted in Figure 2 to make a very intriguing point. In many types of high transactional environments, RAID adapter vendors often optimize hard drive access in what’s called “short stroking” – using a small portion of the drive, usually just the outer tracks, to minimize head movement and thereby minimize seek and access time and increase the performance.
Short version of short stroking story and SSDs: You can take a reasonable capacity, reasonable speed hard drive and short stroke it at 8 percent (and effectively but not physically toss the other 92 percent of the drive), and put a bunch of those together to get the capacity you need (but each drive still consumes its full operational wattage). This gives you a pretty good transactional performance figure at a reasonable price point because hard drives at the non-bleeding edge are inexpensive.
Or, as the diagram implies, you can buy a lot fewer SSDs for about the same total cost as the hard drive farm, fully utilize their capacity, and get 10x the IOPS for 1/20th of the power. Your cost per I/O or I/O per watt metrics with an SSD RAID system just got hugely optimized.
Yes, this applies to a specific situation where short stroking is employed and a major portion of the hard drive isn’t used, but it’s a real-world situation. Short stroking in the range of 8 to 12 percent isn’t uncommon at all in RAID configurations, and going far beyond that uses more of the drive but presents diminishing and even negative returns in IOPS.
If your application resembles this scenario – and I can think of many embedded apps storing a lot of data and needing lightning-fast transactional access that could – this is potentially a big power win and a deeply green way to use RAID and SSDs. Cameron and the PMC-Sierra team are onto something.
In which applications would this solution work for you? E-mail me at ddingee@opensystemsmedia.com or tweet me at @dondingee and share your ideas.
