[Beowulf] Consumer vs. Enterprise Hard Drives in Clusters

[Bill Broadley]

The differences I've seen between "raid edition" drives and regular drives are:

* Dramatically better vibration resistance.  If you are going to bolt a drive
  or two into a desktop it doesn't matter so much.  If you are going to plug
  a drive into a 16 bay enclosure or even into a 1U node with a ton of fast
  fans you might well see a large performance difference because of the
  vibration.  The specification sheets do reflect this btw, I assume this
  is mostly lower density platters and stronger motors for positioning
  the heads.  This is especially noticeable on the consumer drives with the
  higher density platters (375-500GB per platters).  I've seen consumer
  drives that manage 120MB/sec drop to a noisy fluctuation between 18-30
  MB/sec because of vibration

* Consumer drives (at least the non-media ones) often have occasional
  thermal recalibrations.   This seems better these days, but last thing
  you want is a recal triggering a degraded array.

* Consumer drives will go to heroic efforts to read a bad sector, exactly
  the opposite of what you want in a RAID drive.  In a RAID it's better to
  fail and yell bloody murder... especially when the rereading a sector
  a bunch causes the raid to time out and drop the disk.

Of course manufactures claim various things about error rates per billion
bits, designed duty cycles (40 hours a week vs 24/7), improve temperature
envelops, and related.  Alas while this is nice to hear I've not seen any
direct results because of it.

As an example, 500GB wd caviar $64.99, 500GB WD RE3 $89.99.  IMO if you are
building a raid or heavily used 1U with a ton of fans the extra $25 is worth it.