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Boston Linux and Unix InstallFest XXXII Saturday February 28, 2009

Jerry Natowitz wrote:
> BTW: I just started on this list, and caught the tail end of a thread on 
> RAID.  I'd just like to add my $0.02:
> A year or two ago Google published results of a big study they did on 
> disk reliability.  I don't remember much about it, except that they 
> found that RAIDs are usually built using disks from the same 
> manufacturing lot, and that failure modes are often quite similar for 
> disks from a particular lot.  This results in a higher probability than 
> expected that a disk failure will involve multiple drives.
> I read this to mean that RAID 6 or RAID 1+0 (sometimes called 10), or 
> possibly 5+0 should be used rather than RAID 5.

It might also mean that it's a good idea to intentionally mix up your 
drives. Use some that were bought at different times, or from different 
distributors, or perhaps even include more than one manufacturer's drive 
in your array. Commercially sold RAID systems aren't likely to do any of 
those things, but if you build one yourself you can.

My cobbled-together RAID 5 media server gets it right; it's got WD, 
Seagate, and Maxtor (from before the Seagate buyout) drives, and no two 
of the five were bought together. Two of the drives are slightly larger 
than the other three (they're nominally 200GB drives but two are about 
5GB bigger than the others); they contain the RAID 1 boot partition 
along with pieces of the RAID 5 media partition.

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