On Sat, Aug 05, 2017 at 12:58:15PM -0400, Neal Gompa wrote:
> On Sat, Aug 5, 2017 at 8:12 AM, Richard W.M. Jones <rjo...@redhat.com> wrote:
> > On Fri, Aug 04, 2017 at 06:00:58PM +0200, František Zatloukal wrote:
> >> Some insight why was BTRFS dropped by RH:
> >> https://news.ycombinator.com/item?id=14907771
> >>
> >> Also check out Stratis:
> >> https://fedoraproject.org/wiki/Changes/StratisStorage
> >
> > Stratis is a management tool that makes it a bit easier to manage all
> > the layers together.
> >
> > Another aspect which seems indicative of Red Hat's direction [I have
> > no inside information on strategy] is the recent acquisition of
> > Permabit (http://permabit.com/).  AIUI it's a device mapper module
> > which does some clever data deduplication and/or compression across LVs:
> >
> > https://www.theregister.co.uk/2016/06/29/permabit_offering_dedupe_to_linux_masses_almost/
> >
> There are plenty of "clever" kernel modules that do bits and pieces of
> what Btrfs offers. For example, the place I work for created a kernel
> module that makes it possible to do VSS/CoW like snapshotting with
> *any* legacy file system (as long as it has a real block device)
> called dattobd:
> https://github.com/datto/dattobd

That's actually something we could really use and the missing
piece I've been looking for, to do "live" virt-p2v :-/

> It can enable snapshotting for legacy file systems like ext4, xfs,
> jfs, etc. whether it's on LVM or not. It can also back up filesystems
> on things like LVM or mdraid.
> That being said, I've been told that it's unlikely that such
> functionality will ever make it into the Linux kernel itself, and it's
> not as smooth as if the filesystem itself is able to do these things
> (like with Btrfs). The biggest pitfall of this approach? The
> filesystem has to be "frozen" for a small period of time while the
> snapshot is being taken. It's quite noticeable when you're using it on
> an hourly schedule, but it's minimized to the littlest effect possible
> without a filesystem like Btrfs.

I totally accept your point that it's better integrated in the

OTOH back to the P2V case, being able to snapshot arbitrary
filesystems (which as you say Windows can already do with VSS) is
brilliant.  Did they ever try to get this upstream?

> The effect is similar when using LVM snapshots. Stratis is even less
> useful than dattobd because it requires building the storage up in
> that way, whereas dattobd works with existing installations and Btrfs
> can be seeded from existing filesystems and from there you can
> leverage all the benefits of Btrfs.


Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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