Save the planet – buy fatter disks and flash

Hard drive capacity overt time (from commons.wikimedia.org) (cc)
PC hard drive capacity over time (from commons.wikimedia.org) (cc)

Well maybe that overstates the case but there is no denying that both fatter (higher capacity) drives and flash memory (used as cache or in SSDs) saves energy in today’s data center.  The interesting thing is that the trend to higher capacity drives has been going on for decades now (see chart) but only within the last few years has been given any credit for energy reduction.  In contrast, flash in SSDs and cache is a relative newcomer but saves energy nonetheless.

I almost can’t recall when disk drives weren’t doubling in capacity every 18 to 24 months.  The above chart only shows PC drives capacities over time but enterprise drives have followed a similar curve.  The coming hard drive capacity wall may slow things down in the future but just last week IBM announced they were moving from a 300GB to a 600GB 15Krpm enterprise class disk drive in their DS8700 subsystem.  While doubling capacity may not quite halve energy use, it’s still significant.   Such energy reductions are even more dramatic with slower, higher density disks. These SATA disks are moving from 1TB to 2TB later this year and should cut energy use considerably.

Similarly, NAND flash density used in SSDs is increasing capacity at almost a faster rate than disk storage.  ASIC feature size continues to shrink and as such, more and more flash storage is packed onto the same die size.  Improvements like these are doubling the capacity of SSDs and flash memory.  While SSD power reduction due to density improvements may not be as significant as disk, we hope to see a flattening out of power use per NAND cell over time.  This flattening out of power use is now happening with processing chips and we see little reason why similar techniques couldn’t apply to NAND.

But the story with flash/SSDs is a bit more complicated:

  • SSDs don’t consume as much energy as a standard disk drive at the same capacity, so a 146GB enterprise class SSD should consume much less energy than a 146GB enterprise class disk drive.
  • SSDs don’t exhibit the significant energy spike that hard disk drives encounter when driven at higher IOPs and was discussed in SSDs vs. Drives energy use.
  • SSDs can often replace many more disk spindles than pure capacity equivalence would dictate.  Some data centers use more disks than necessary to spread workload performance over more spindles wasting storage, power and cooling.  Moving this data to SSDs or adding flash cache to a subsystem, spindle counts can be reduced dramatically and as such, slash energy use for storage.

All this says that using SSDs or flash in place of disk drives reduces data center power requirements.  So if you’re interested in saving energy and thus, helping to save the planet, buy fat(ter) disks and flash for your data storage needs.

Brought to you on behalf of Planet Earth in honor of Earth Day.

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