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:


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.

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.

真実はいつも一つ!/ Always, there's only one truth!
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