[linux-lvm] Why does thinpool take 2*poolmetadatasize space?

[Zdenek Kabelac]

Dne 20. 10. 20 v 18:33 Scott Moser napsal(a):
> When I create an lvmthinpool with size S and poolmetadatasize P,
> it reduces the available freespace by S+2P. I expected that to
> be S+P. Where did the extra poolmetadatasize get used?
> 
> See below for example.
> before lvcreate we had 255868 free, after we had 254588.
> The difference is 1280.  (1024 + 2*128).
> 


lvm2 preallocated hidden _pmspare volume which has the size of
biggest metadata LV in a VG.

Such LV is used for automated 'lvconvert --repair'.

If you don't want this LV to be created you can add

--poolmetadataspare y|n

but in this case you are fully in your own to figure out,
where to take the space for repaired metadata.

You can also at any time lvremove _pmspare LV if necessary.

Regards

Zdenek