Re: ZFS kernel panic

The simplest thing to do in case of a write error is to
simply ignore it. You *will* catch this problem when you try
to read this block. One step better is to do what you
suggest.

You can't ignore write error, because application already assumed the
write succeeded, which can lead to misbehaviour later. ZFS cannot yet
handle write error, so it panics to preserve data consistency. This is
the good reaction on ZFS side until skipping bad blocks is not
implemented.

If you ignore a write error, the effect is the same as if the
disk block was good on writing but went bad before the first
read. Seems to me this is better than panicing (but of
course not as good as finding an alternate block).

AFAIK ZFS already uses redundancy for metadata so the
metadata consistency will be maintained.

What happens now when you do use redundancy and there is a
write error while writing one of the copies? Does the system
panic or is this error ignored?

Don't remember off hand, but component is probably marked as bad and
vdev group goes to degraded state. You can simulate this easly with
gnop(8).

Thanks. It would be good to add some ioctl to allow failing
specific blocks on reads and/or writes.
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