Re: [PATCH v2 00/10] fsdax,xfs: Add reflink&dedupe support for fsdax
On Sat, Mar 13, 2021 at 11:24:00AM -0500, Neal Gompa wrote:
On Sat, Mar 13, 2021 at 8:09 AM Adam Borowski
<kilobyte(a)angband.pl> wrote:
>
> On Wed, Mar 10, 2021 at 02:26:43PM +0000, Matthew Wilcox wrote:
> > On Wed, Mar 10, 2021 at 08:21:59AM -0600, Goldwyn Rodrigues wrote:
> > > DAX on btrfs has been attempted[1]. Of course, we could not
> >
> > But why? A completeness fetish? I don't understand why you decided
> > to do this work.
>
> * xfs can shapshot only single files, btrfs entire subvolumes
> * btrfs-send|receive
> * enumeration of changed parts of a file
XFS cannot do snapshots since it lacks metadata COW. XFS reflinking is
primarily for space efficiency.
A reflink is a single-file snapshot.
My work team really wants this very patchset -- reflinks on DAX allow
backups and/or checkpointing, without stopping the world (there's a single
file, "pool", here).
Besides, you can still get poor-man's whole-subvolume(/directory)
snapshots by manually walking the tree and reflinking everything.
That's not atomic -- but rsync isn't atomic either. That's enough for
eg. dnf/dpkg purposes.
Meow!
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