Are enterprise drives worth the power?
Data center power consumption is getting a lot of press play lately. The issue: increased density means that a data center rack that used to need a 2kw may now need 6kw. And for every dollar spent to power equipment, another 40 cents is spent on cooling that equipment. It is a real problem.
Storage: power hog?
Most of the published press concern seems to focus on pizza boxes and blade servers, not big iron arrays, probably because Google raised the issue years ago. Yet EMC is responding with a couple of technical marketing papers (see Power Efficiency and Storage Arrays and EMC Symmetrix DMX-3 Electrical Power Estimation and Configuration Planning. HDS doesn’t seem to have any papers addressing the issue.
Feets, do your stuff
Nice tap dance by EMC in the latter paper. The simple fact is that all 3.5″ drives used in big iron arrays are power hogs. Fibre Channel alone adds about 2 watts per drive, according to Seagate’s Cheetah data sheet, which isn’t too surprising when you consider that FC drives have two interfaces. Even 7200 RPM SATA desktop drives use about 12 watts instead of FC 15k drives 16 watts. And it looks like SATA interfaces are slightly less power-efficient than PATA drives – on the order of 5% – while SAS drives are even worse – about 40% higher than SCSI. Oops!
So what is a “green” array vendor to do?
Seagate thinks it has the answer in their new Savvio 2.5″ enterprise drives. At 8 watts they use about 40% less power than equivalent 3.5″ drives. Of course, they are 70% smaller, so vendors will be able to cram even more drives into a smaller box, increasing power use per rack.
Maybe it’s time to get back to RAID
Striping was the original performance hack for disks. To my mind, the storage power problem isn’t going to get much better until vendors start using disks that were designed from the ground up for low power consumption: notebook drives. These average about 3 watts each and are designed to be shut down frequently. While each drive is pretty slow, stripe across a half dozen or so and the performance is better than you could buy 15 years ago. Didn’t people have databases and OLTP 15 years ago?
Or for a really radical solution. . .
Flash-based SSDs are even more frugal – at least in power – using a fraction of even the best notebook drive’s power. Perhaps the day will come when a data center will be cooled by a couple of room-size air conditioners and Samsung will be selling a couple of hundred million enterprise flash drives a year.
Comments welcome of course. And for all you Americans out there, don’t forget to vote tomorrow, Tuesday, November 7th.