2011-12-19 2:53, Jan-Aage Frydenbø-Bruvoll пишет:
On Sun, Dec 18, 2011 at 22:14, Nathan Kroenert<nat...@tuneunix.com>  wrote:
Do you realise that losing a single disk in that pool could pretty much
render the whole thing busted?

Ah - didn't pick up on that one until someone here pointed it out -
all my disks are mirrored, however some of them are mirrored on the
controller level.

The problem somewhat remains: it is unknown (to us and to ZFS)
*how* the disks are mirrored by hardware. For example, if a
single-sector error exists, would the controller detect it
quickly? Would it choose the good copy correctly or use the
"first disk" blindly, for the lack of other clues?

Many RAID controllers are relatively dumb in what they do,
and if an error does get detected, the whole problematic
disk is overwritten. This is long, error-prone (if the other
disk in the pair is also imperfect), and has a tendency to
ignore small errors - such as those detected by ZFS with
its per-block checksums.

So, in case of one HW disk having an error, you might be
having random data presented by the HW mirror. Since in
your case ZFS is only used to stripe over HW mirrors,
it has no redundancy to intelligently detect and fix
such "small errors". And depending on the error's
location in the block tree, the problem might range
from ignorable to fatal.


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