Conversion LVM to LVM thin

[SysAx]

Hi,

I have a cluster Promxox 4.2 with 4 nodes. One of this nodes is installed under ZFS local storage and the others under LVM default storage.

The snaphot backup mode are working well with ZFS but it is not possible with LVM.

On another independant host (not a part of the cluster), i tried to transform LVM to LVM thin ( https://forum.proxmox.com/threads/best-way-to-convert-lvm-to-lvm-thin.27204/#post-136968) and now the snaphots are possible.

Is it possible to do the same thing on each nodes with LVM, without to have to re-install the cluster ?

What is the best way to proceed and the safest ?

Best regards,

Christian

 

[boopzz]

Can I bump this as I want to know.

I converted my LVM storage to LVM-thin but it was empty, Im trying to understand how it works. Does it add a Volume Group or does it add a thin provisioned Logical Volume and use disks on that?

 

[wbumiller]

I converted my LVM storage to LVM-thin but it was empty

Are you saying you lost data or are you just surprised that eg. the `lvs` output hasn't changed (much). How did you perform the conversion? (I saw the instructions in post linked by the OP tell you to migrate all the guests away from it first, so I hope your data's fine at least).

Im trying to understand how it works. Does it add a Volume Group or does it add a thin provisioned Logical Volume and use disks on that?

While LVM-thin can be used similar to a volume group it itself consists of two regular logical volumes on an existing volume group. One for the data and one for the metadata. These two volumes are grouped together as a "thin pool" (visible in the lvs output marked with a 't' as the first attribute letter), and thin volumes are created "inside" the pool. They appear in lvs as belonging to the same volume group as the pool, stating the pool's name in the Pool column, and marked with a 'V' attribute.
This means there can be multiple thin pools in a single volume group.
Finally, in PVE when you create the storage you have to select both the volume group and the thin pool. The GUI contains drop down boxes for both and once you select a volume group it should only show you actual thin pools found on that VG in the second box.

 

[boopzz]

Are you saying you lost data or are you just surprised that eg. the `lvs` output hasn't changed (much). How did you perform the conversion? (I saw the instructions in post linked by the OP tell you to migrate all the guests away from it first, so I hope your data's fine at least).

Im saying the LV that I converted was empty to start with.

I've since stopped being lazy and read up . So you modify an existing LV to be an LVM-Thin or create a new LV as a thin-pool, you then create a disk "within" that thin-pool.

Thanks for the added info though, much appreciated and good to know a little bit more on how it relates to Proxmox.