On Wed, 2006-09-13 at 02:30, Richard Elling wrote:
> The field data I have says that complete disk failures are the exception.
> I hate to leave this as a teaser, I'll expand my comments later.
That matches my anecdotal experience with laptop drives; maybe I'm just
lucky, or maybe I'm just paying attention than most to the sounds they
start to make when they're having a bad hair day, but so far they've
always given *me* significant advance warning of impending doom,
generally by failing to read a bunch of disk sectors.
That said, I think the best use case for the copies > 1 config would be
in systems with exactly two disks -- which covers most of the 1U boxes
out there.
One question for Matt: when ditto blocks are used with raidz1, how well
does this handle the case where you encounter one or more single-sector
read errors on other drive(s) while reconstructing a failed drive?
for a concrete example
A0 B0 C0 D0 P0
A1 B1 C1 D1 P1
(A0==A1, B0==B1, ...; A^B^C^D==P)
Does the current implementation of raidz + ditto blocks cope with the
case where all of "A", C0, and D1 are unavailable?
- Bill
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