[linux-lvm] resize of thin pool

[Michael Ryan]

Hi all. Couple quick questions.


1. It is possible to resize (grow and shrink) the size of an active thin pool?


2. What limitations exist on a thin volume with an external origin? I understand the origin volume is effectively read-only, but can the thin volume be written to? How about a snapshot of the thin volume with the external origin?


Thanks much.
- Michael

[Zdenek Kabelac]

Post by Michael Ryan
Hi all. Couple quick questions.
1.It is possible to resize (grow and shrink) the size of an active thin pool?

Only extension of thin pool is supported (offline/online).
You cannot shrink the thin pool size.

(Theoretically you could relatively easily defragment chunks offline and
update mapping, but this is not yet supported...)

Post by Michael Ryan
2.What limitations exist on a thin volume with an external origin? I
understand the origin volume is effectively read-only, but can the thin volume
be written to? How about a snapshot of the thin volume with the external origin?

External origin has to be activated as a read-only volume.

The same external origin can be shared by many thin volumes even from
different pool volumes. Of course you could then snapshot such thin volume as
any other thin volume (i.e. chaining snapshot of snapshot of snapshot).
External origin can be still used as read-only normal LV and also it may be
used as the origin for old-style traditional snapshot at the same time.

Current limitation is - you can't merge changes from your thin volume back
to your external origin (it's planed to add this feature in the future...)
Then there are some enforced limitation of the size alignments.

Zdenek