Re: Converting thin stripe volume to linear

[Zdenek Kabelac <zdenek.kabelac@gmail.com>]

Dne 14. 03. 25 v 1:17 Patrick Hemmer napsal(a):
> 
> On Thu, Mar 13, 2025, at 20:05, Zdenek Kabelac wrote:
>> Dne 14. 03. 25 v 0:14 Patrick Hemmer napsal(a):
>>> On Thu, Mar 13, 2025, at 14:54, Zdenek Kabelac wrote:
>>>> Dne 13. 03. 25 v 1:38 Patrick Hemmer napsal(a):
>>>>> I've got a LVM thin stripe volume across 2 drives that I'm trying to migrate to a new larger single drive (getting rid of the old drives). Following various information on the subject, it seems the procedure here is to first convert from stripe to mirror, and then from mirror to linear. While attempting this, I seem to have hit an issue on the second part of that process, and am not having much luck resolving it.
>>>>
>>>> Hi
>>>>
>>>> Likely you can convert your nearly full thin-pool with a single thin volume to
>>>> a linear  LV by just taking  'dd' copy of  if=/dev/thin of=/dev/linear - using
>>>> direct io option (and this can be actually faster then raid mirroring).
>>>
>>> I assume I need to copy both the tdata and tmeta volumes to their new linear counterparts. Did this, but now I assume I need to do something to get lvm to rescan the new linear thin volume to pick up the logical volumes that are now on it. And also stop LVM from picking them up off the old thin volume. I deactivated the old thin volume, but LVM is still recognizing up all the logical volumes inside it. I could completely delete the old thin volume, but I'd prefer to get the new volume online before doing that.
>>>
>>
>> Hi
>>
>> Thin volume is using thin pool that is using data & metadata.
>>
>> Thus thin-pool can remain active even when thin LV is already deactivated,
>> depends on the use case - and you can obviously deactivate also your thin-pool.
>>
>> In your case you need to 'forget' copying thin_tdata or thin_tmeta or even
>> thin-pool ssd/thin itself.
>> Your 'lvs -a'  you've shown unfortunately  lists *ONLY* thin-pool  (ssd/thin)
>> but not a single thin LV  (with letter 'V' in attributes and using 'ssd/thin'
>> as Poll volume)
>>
> Yes, I mentioned a couple times in the first email that there are many volumes which sit on top of the thin volume, but which I omitted. And that I did not want to copy them manually, because there's a lot of them, and many of them are snapshots. So to recreate the snapshots, I'd have to copy the oldest snapshot to the new thin volume, snapshot it, copy the next oldest, etc down the line. That would be a very time consuming and painful process. Hence why it's not under consideration.


Then you are using somewhat  confusing terminology.

If you want to convert  thin  to linear - it means you no longer want it would 
a thin volume.

For this you need to copy 'dd'  thins you want to convert - and obviously if 
you had 300G thinLV + 300G snapshot thinLV -  you need  600G to store them in 
linear volumes.

If you want to something different you will need to desribe things differently.

Buf if you do not want to use thin-pool with your new storage - then use 'dd' 
copy

If you want to however just 'migrage' thin-pool to a new PV  - then you can 
simply  'vgextend'  new drive to your existing VG.
Then  pvmove  /dev/old  /dev/new
lvm2 will figure out how to do a mirroring.
Once this all is finished you simply 'vgreduce' your old PV from this VG.

Regards

Zdenek