Disk Mirroring (was Re: Altos 5000)

[Frank I. Reiter]

In article <3895 at altos86.Altos.COM> dtynan at altos86.Altos.COM (Dermot Tynan) writes:
>
>See above.  Nobody is trying to produce a fault-free system.  We are just
>trying to reduce the likelihood of having to restore a filesystem.  Believe
>me.  Disk mirroring will slow down disk writes (which aren't the bulk of
>disk operations, anyway), but it will double your disk reliability.

Maybe I've missed something, but it seems to me that the results should be
orders of magnitude better than that.  Let's say that the odds of a particular
drive failing on a particular day are 1 in 1000.  The odds of both drives
failing on that day are then 1 in 1000000 are they not?  Does not mirroring
mean that both drives must fail simultaneously in order for there to be loss
of data?
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