[nSLUG] hard disks can't be trusted (as if you didn't already know that)

Stephen Gregory nslug at kernelpanic.ca
Sun Mar 4 18:19:05 AST 2007

On 4-Mar-07, at 16:27 , George N. White III wrote:

> Google's study is for consumer grade disks, but their overall  
> failure rates aren't out of line with other studies.

The Google study is interest, but there is a slight problem: they  
don't distinguish between failure types. The study study states that  
failures such as controller failure were also counted as drive  
failures. This does not make the study worthless, but the conclusions  
should be more along the lines of: "more study needed." Probably the  
most interesting aspect of the study is that SMART is a poor  
indicator of drive health.

A Carnegie Mellon U study published at the same conference is also  
interesting. They also found no bath-tub effect. They found that  
failure rates were significantly higher then manufacturers claims.  
The study found no correlation between failure and SCSI, FCAL, or  
SATA. However it is not clear if the SATA drives are desktop drives  
or server grade "near-line" drives.


I definitely want to see more studies on consumer grade versus server  
grade drives. In the lab we have two Sun raid arrays and we had an  
Apple raid. Sun uses stupid expensive SCSI drives. Apple uses cheap  
desktop (not even semi-server) IDE drives in FCAL to IDE sleds. The  
drives in the Apple raid failed so often that it was decommissioned  
in less then a year. There are twice as many SUN drives in operation  
since 2001 and I think only one drive has ever failed. Obviously  
there are not enough drives to draw any conclusions from, but it has  
made us reconsider using cheaper desktop hard drives. (It doesn't  
hurt that SUN, IBM, Dell, and HP will courier a drive to me in 1 day  
and Apple won't.)



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