Hammer2 offline deduplication

[Justin Sherrill]

Are you looking for how it works technically, or how to operate it?
The design document goes into the technical details of how it's set
up:

http://gitweb.dragonflybsd.org/dragonfly.git/blob_plain/HEAD:/sys/vfs/hammer2/DESIGN

The design notes mention that, like you say, online dedup is on by
default.  There's no utility to run it offline yet, though I don't
know how much of a difference that makes in practice; online dedup may
already do most of the work.   I'd be interested in statistics on
that.

On Wed, Nov 6, 2019 at 2:25 PM Mikhail Novosyolov
<m.novosyolov at rosalinux.ru> wrote:
>
> Hi,
>
> I have not been able to find documentation about how deduplication works
> in Hammer2. I have only found that online deduplication is now on by
> default, but there seems to be no description how it works.
>
> Is it possible to make offline deduplication? I mean finding blocks with
> the same checksum and making one block point to another instead of
> spending space on disk twice? There are several utilities that do this
> on BTRFS in Linux, for example https://github.com/Zygo/bees
>