[ClusterLabs] OCFS2 fragmentation with snapshots

[Andrei Borzenkov]

On Tue, May 18, 2021 at 1:52 PM Ulrich Windl
<Ulrich.Windl at rz.uni-regensburg.de> wrote:
>
> Hi!
>
> I thought using the reflink feature of OCFS2 would be just a nice way to make crash-consistent VM snapshots while they are running.
> As it is a bit tricky to find out how much data is shared between snapshots, I started to write an utility to examine the blocks allocated to the VM backing files and snapshots.
>
> Unfortunately (as it seems) OCFS2 fragments terribly under reflink snapshots.
>

Does it cause any real problem?
...
>
> So I wonder (while understanding the principle of copy-on-write for reflink snapshots):
> Is there a way to avoid or undo the fragmentation?
>

If you understand the principles you can answer it yourself. To avoid
fragmentation you need to avoid reflink.