Borja Marcos via freebsd-stable wrote:
On 8 May 2019, at 05:09, Walter Parker <walt...@gmail.com> wrote:
Would a disk rescue program for ZFS be a good idea? Sure. Should the lack
of a disk recovery program stop you from using ZFS? No. If you think so, I
suggest that you have your data integrity priorities in the wrong order
(focusing on small, rare events rather than the common base case).
ZFS is certainly different from other flesystems. Its self healing capabilities
help it survive problems
that would destroy others. But if you reach a level of damage past that
“tolerable” threshold consider
yourself dead.
bingo.
Is it possible at all to write an effective repair tool? It would be really
complicated.
which is why I don't think a 'repair tool' is the correct way to go.. I
get the ZFS devs saying 'no' to it, I really do. A tool to scan and
salvage (if possible) the data on it is what it needs I think... copy
off, rebuild the structure (reformat) and copy back. This tool is what I
was pointed at: https://www.klennet.com/zfs-recovery/default.aspx ... no
idea if it works yet.. but if it does what it says it does it is the
'missing link' I'm looking for... just I am having issues getting
Windows 7 with SP1 on a USB stick to get .net 4.5 on it to run the
software... :/ (only been at it 2 days though, so time yet.)
By the way, ddrescue can help in a multiple drive failure scenery with ZFS.
Been there done that - that's how I rescued it when it was damaged in
shipping.. though I think I used 'recoverdisk' rather than ddrescue ...
pretty much the same thing if not the same code. sector copied all three
dead drives to new drives, put the three dead back in, brought them back
online and then let it resilver... the data was recovered intact and not
reporting any permanent errors.
If some of the drives are
showing the typical problem of “flaky” sectors with a lot of retries slowing
down the whole pool you can
shut down the system or at least export the pool, copy the required drive/s to
fresh ones, replace the
flaky drives and try to import the pool. I would first do the experiment to
make sure it’s harmless,
but ZFS relies on labels written on the disks to import a pool regardless of
disk controller topology,
devices names, uuids, or whatever. So a full disk copy should work.
Don't need to test it... been there done that - it works.
Michelle, were you doing periodic scrubs? I’m not sure you mentioned it.
Yes though once a month as it took 2 weeks to complete.
Michelle
--
Michelle Sullivan
http://www.mhix.org/
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