ZFS scrub/selfheal not really working

[James R. Van Artsdalen]

Andrew Snow wrote:
> It seems like its a good idea to chuck out the whole lot, after first
> double-checking or replacing your controller, cabling, and power
> supply.  ZFS can't help you :-)

No, don't throw bad hardware away!  Save it for testing - it's much
harder to find hardware with intermittent failures that may be useful
for testing than hardware that is dead or doesn't fail in a short amount
of time.

>> So, my question is why doesn't ZFS rewrite those sectors with READ
>> errors during scrub?
>
> Because of the transactional nature of ZFS it writes the fresh data in
> a different part of the disk and then marks the old bad sectors as free.

The old sectors are not freed if they are referenced by snapshots or
clones.  Vacating a block would be a very expensive operation for ZFS in
the general case.