[ClusterLabs] OCFS2 fragmentation with snapshots

Andrei Borzenkov arvidjaar at gmail.com
Tue May 18 07:05:47 EDT 2021

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.

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