[dm-devel] Reducing size of thin spare metadata, thin metadata

[Patrik Horník]

Hi,

2014-10-06 9:39 GMT+02:00 Zdenek Kabelac <zkabelac at redhat.com>:
> Dne 6.10.2014 v 09:28 Patrik Horník napsal(a):
>
>> Hi,
>>
>> is it possible to (safely) reduce size of thin metadata and / or thin
>> spare metadata? What size of spare metadata is needed? Can it be
>> smaller than size of pool metadata?
>>
>
> You could remove pool spare volume anytime  - lvremove.
> (it's only used for automated lvconvert --repair)
>
> Repair needs free space in VG - if there is no free space - well tool can't
> be used.

when does automated lvconvert --repair kick in? Can I do it manually
if it cannot continue automatically? (I actually have space for spare
metadata so I want it there if it useful but smaller. I only need to
decrease size of my volume group by couple of 100s MB because of
moving to new device. My spare is 8 GB as is regular metadata.)

> You could also reduce size of thin pool metadata in case it's too big, just
> not online.
>
>
> With offline thinpool with these manual steps
> (will be later automated with tool as well):
>
> --
>
> make a temporary LV of any size.
> swap this temp LV with  pool metadata
>
> # lvconvert --thinpool  vg/mypool   --poolmetadata mytemplv
>

Does not lvconvert only change metadata volume not copying data to it?
So isn't there missing step to copy metadata from current metadata to
mytemplv? Why do u use mytemplv anyway and dont copy metadata directly
from current metadata to new smaller LV?

Anyway I prefer to reduce spare metadata if possible and not risk
reducing real metadata, it should be enough for me.

Thanks.

Patrik

> Create your volume for metadata with new reduced size
> (unsure which size is your target - but some calcs based on estimated usage
> are necessary)
>
> Activate   mytemplv  which has now real metadata from thinpool.
>
> # thin_repair  -i /dev/vg/mytemplv   -o /dev/vg/mynewsizemeta
>
> # thin_check  /dev/vg/mynewsizemeta
>
>
> If all is green - swap new meta into your thinpool
>
> # lvconvert --thinpool  vg/mypool   --poolmetadata mynewsizemeta
>
>
> If all works great you are done :)
> In all other cases you have your backup at hand :)
>
> Yeah - you still have old metadata in mytemplv - this volume you may remove
> later if all works well - otherwise you may try to swap this volume back.
>
> Zdenek
>