[linux-lvm] Data percentage too large after thin_dump --repair/thin_restore

[Timur Alperovich]

Thanks for the reply Zdenek!

I realized that the biggest confusion for me is that I'm using LVM2 tools
2.02.98-6 (which is the latest version in Ubuntu) and the swapping support
was added in 2.02.98-9 (I'm curious why they didn't pick the latest of
2.02.98).

On Tue, Sep 2, 2014 at 2:06 AM, Zdenek Kabelac <zkabelac at redhat.com> wrote:

> Dne 1.9.2014 v 20:13 Timur Alperovich napsal(a):
>
>  Hi there,
>>
>> I'm using LVM 2.02.98 and encountered a metadata corruption issue. To
>> recover
>> from it, I attempted to perform the following steps:
>> 1. thin_check /dev/mapper/pool_tmeta
>> 2. thin_dump /dev/mapper/pool_tmeta > /tmp/metadata
>>
>
> Hi
>
> NEVER EVER use _tmeta device from running active thin-pool volume.
> It's the very same case like you would be running  'fsck' on
> a mounted filesystem.

 3. dd if=/dev/zero of=/dev/mapper/pool_tmeta
>> 4. thin_restore -i /tmp/metadata -o /dev/mapper/pool_tmeta
>>
>> All of the above steps have succeeded, however, when attempting to list
>> the
>> _metadata\_percent_ field, I get an error:
>>
>
> I'm surprised you've not got kernel OOPS after such brutal destruction
> of life metadata device (i.e. almost equal to zeroing your root volume).
>
>
>  Is this a known issue and is there a workaround? I need to be able to
>> examine
>> the _metadata\_percent_ field to make sure we don't exhaust the metadata
>> space.
>>
>>
> Normal way -
>
> lvconvert --repair vg/pool
>

I believe this was added in 2.02.102. Unfortunately, upgrading LVM2 is a
bit tricky on Ubuntu (will need to build the package from source).


>
>
> If this is not working - then you can 'swap' metadata out of your thin-pool
> using following sequence-
>
> - make sure pool is not active.
> - build temporary local LV   (lvcreate -l1 vg -n temp)
> - swap this LV with metadata of to-be-repaired pool
>   (lvconvert --thinpool vg/fixpool --poolmetadata temp)
>

This command fails, as --poolmetadata is not a valid option. I found that
the swapping was not supported until 2.02.98-9 and I'm using 2.02.98-6 (in
2.02.98-9 changelog: "Add lvconvert support to swap thin pool metadata
volume."). Is there a way to do this without the swapping support? I guess
I should be able to do it with dmsetup? I'm not sure how painful that would
be.

I'll look into upgrading the version, as well (which is probably the right
thing to do).

- activate 'temp' LV now with pool's metadata

  (lvchange -ay vg/temp)
> - repair metadata
>   (you may need other 'bigger' volume to restore fixed metadata)
>   (i.e.  thin_restore -i /dev/vg/temp -o /dev/vg/biggertemp)
> - thin_check restored volume
> - thin_dump - and compare  vgcfgrestore & this dump are at the same
>   transaction_id state (look at lvm2 metadata for thin pool)
> - deactivate again related volumes
> - swap repaired LV back
>   (lvconvert --thinpool vg/fixpool --poolmetadata repairedtemp)
> - try to active repaired thin pool
> - remove unneeded volumes from vg....
>
>
> Zdenek
>
>
>
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> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
>

Timur
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