[Beowulf] what defines "enterprise class" hard drives?

[Joe Landman]

On 08/05/2010 05:47 PM, Rahul Nabar wrote:
> I wanted to buy some 1 Terabyte SATA drives for our storage array and
> wanted to stay away from the cheap desktop stuff. But each
> manufacturer has some "enterprise class drives". But is there
> something specific to look for? Most of those seem to have a MTBF of
> around 1.2 million hours and a URE of about 1 in 10^15. The S.M.A.R.T.
> abilities seem fairly standard.  Is there a list somewhere of well
> tested drives? Or any recommendations?
>

Understand that these designations have more to do with product feature 
set groupings (marketing groupings) than anything else.  The feature set 
variations are mostly in the firmware for large groups of product 
offerings (lowers BOM costs by using the same physical hardware on all 
units).

A "desktop" drive will work much harder to recover an error than an 
"enterprise" drive.  The former is assumed not to be in a RAID so that 
it has to handle errors itself, and the latter is assumed to pass errors 
up to a RAID controller.

The head settling logic (not head hardware) may be different, as 
"desktop" drives, again, assumed not to be in RAIDs, shouldn't have to 
worry about all the vibration maxima at 120Hz, 166.7Hz, and 250Hz (for 
7200, 10k and 15k RPM drives), or their beat frequencies and octaves. 
"Enterprise" drives have to worry about insufficient vibration damping, 
so the firmware pack could have a different head settling/seeking code 
within it.

"Desktop" drives are assumed to not be spinning 24x7, and have some 
interesting power down capabilities, which are anathema to many RAID 
controllers (and MD RAID for that matter).

Can you use "desktop" drives in your RAIDs?  In some cases, yes.  Just 
be careful with this.

This said, I'd strongly recommend extended testing.  As we have 
discovered during some of our testing in this area, some "desktop" (and 
in this vendors case, their "enterprise") drives take ... er ... 
liberties with the specs, and can, and do wreak havoc on RAIDs (which is 
in part why we no longer ship this particular vendor's drives).


-- 
Joseph Landman, Ph.D
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