On Sun, Aug 15, 2010 at 02:26:06PM -0500, Robert Nesius wrote:
> Different performance profiles even though they may support the same specs,
> and also the fact that even drives of the same size may not necessarily have
> the same physical geometries or other physical characteristics.  e.g.,
> different cache sizes - on a mirrored drive maybe one drive has to do a
> cache flush while another one doesn't, thus causing the write to take longer
> simply because one drive could absorb the write without going to the
> platters while the other couldn't.

What?  If I ask "get this on the platter", it better be on a platter,
not in the cache of some smart-less drive, waiting for the power
failure.

>                                     That's assuming you didn't match cache
> sizes, which most people likely would have the sense to not do even if they
> were mixing/matching drives/vendors.

I'm not sure what you mean here.

> My experience in large-enterprise installs is that everyone uses the same
> drives within their arrays and disk cabinets.

My experience with large-scale restaurant operations is that the food
is crap.  What would happen to an admin if 3 out of the 6 drives in a
cabinet fail?  What would happen to the manager who signed the
purchase order for 12 identical drives?  Nothing -- failure has no
consequences.  (I am ignoring the 'find the tape and restore the
stuff'.  Downtime is real money, it must come from somewhere.)

>                                                We didn't experience massive
> simultaneous failures, and the detection/replacement of failed drives was
> just part of the service contract for the hardware.  Originally we would
> replace failed drives and rebuild arrays ourselves, but over the past eight
> years the vendors took that over.


> Lastly, diversifying drive as a risk-mitigation strategy can have the
> opposite effect - one of the mix-in products may be far worse than the
> others.

So you'd rather have 6 identical crappy drives, or a prayer's chance
that at least half are good?

Cheers,
florin

-- 
Bruce Schneier expects the Spanish Inquisition.
      http://geekz.co.uk/schneierfacts/fact/163
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