[linux-lvm] Problem with partially activate logical volume
zdenek.kabelac at gmail.com
Wed Jul 27 19:56:27 UTC 2022
Dne 25. 07. 22 v 16:48 Ken Bass napsal(a):
> (fwiw: I am new to this list, so please bear with me.)
> Background: I have a very large (20TB) logical volume consisting of 3 drives.
> One of those drives unexpectedloy died (isn't that always the case :-)). The
> drive that failed happened to be the last PV. So I am assuming that there is
> still 2/3 of the data still intact and, to some extent, recoverable. Although,
> apparently the ext4 fs is not recognised.
> I activated the LV partially (via -P). But running any utility on that (eg:
> dumpe2fs, e2fsck, ...) I get many of these in dmesg:
> "Buffer I/O error on dev dm-0, logical block xxxxxxx, async page read." The
> thing is, the xxxxxxx block is on the missing drive/pv.
> I have also tried some recovery software, but eventually get these same
> messages, and the data recovered is not really useful.
> Please help! How can I get passed that dmesg error, and move on. 14TB
> recovered is better than 0.
Loosing such a large portion of device is always going to be a BIG problem.
Filesystem spreads metadata all over the place - ExtX is somewhat better then
BTree based FS like XFS,BTRFS and may give you lot of your data back.
But that's why people should never underestimate how important is to keep
reasonable fresh backups of their data - otherwise sooner or later there comes
lesson like this one.
What you could try is to 'add' new PV to VG and use space for taking snapshot
of your LV you want to repair - but this is somewhat complicated as you need
to 'fix' VG first - which would ideally need to have some size of storage you
just lost - but this gives you then fairly easy way forward.
(one way to do this is to use even 'virtual' storage over the loop back device
- but that's for likely skilled admin.)
Lvm2 partial activation is designed to be used in a way to ACTIVATE LV - and
copy the content to better/safe/secure location and there start to recover the
Repairing storage in-place is usually straight road to hell - as there could
be numerous way of recovery to try - but if your 1st. try actually destroys
data even more, you can't retry with different strategy.
So depending on how much money and time you want to put into recovery of your
data there are several different strategies possible - considering storage
space is relatively 'cheap' if your are data are really important.
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