On Thursday, January 06, 2011 22:52:25 Freddie Cash wrote:
> On Thu, Jan 6, 2011 at 1:42 PM, Carl Cook <cac...@quantum-sci.com> wrote:
> > On Thu 06 January 2011 11:16:49 Freddie Cash wrote:
> >> > Also with this system, I'm concerned that if there is corruption on
> >> > the HTPC, it could be propagated to the backup server. Is there some
> >> > way to address this? Longer intervals to sync, so I have a chance to
> >> > discover?
> >>
> >> Using snapshots on the backup server allows you to go back in time to
> >> recover files that may have been accidentally deleted, or to recover
> >> files that have been corrupted.
> >
> > How? I can see that rsync will not transfer the files that have not
> > changed, but I assume it transfers the changed ones. How can you go
> > back in time? Is there like a snapshot file that records the state of
> > all files there?
>
> I don't know the specifics of how it works in btrfs, but it should be
> similar to how ZFS does it. The gist of it is:
>
> Each snapshot gives you a point-in-time view of the entire filesystem.
> Each snapshot can be mounted (ZFS is read-only; btrfs is read-only or
> read-write). So, you mount the snapshot for 2010-12-15 onto /mnt,
> then cd to the directory you want (/mnt/htpc/home/fcash/videos/) and
> copy the file out that you want to restore (cp coolvid.avi ~/).
>
> With ZFS, things are nice and simple:
> - each filesystem has a .zfs/snapshot directory
> - in there are sub-directories, each named after the snapshot name
> - cd into the snapshot name, the OS auto-mounts the snapshot, and off you
> go
>
> Btrfs should be similar? Don't know the specifics.
>
> How it works internally, is some of the magic and the beauty of
> Copy-on-Write filesystems. :)
I usually create subvolumes in btrfs root volume:
/mnt/btrfs/
|- server-a
|- server-b
\- server-c
then create snapshots of these directories:
/mnt/btrfs/
|- server-a
|- server-b
|- server-c
|- snapshots-server-a
|- @GMT-2010.12.21-16.48.09
\- @GMT-2010.12.22-16.45.14
|- snapshots-server-b
\- snapshots-server-c
This way I can use the shadow_copy module for samba to publish the snapshots
to windows clients.
--
Hubert Kario
QBS - Quality Business Software
02-656 Warszawa, ul. Ksawerów 30/85
tel. +48 (22) 646-61-51, 646-74-24
www.qbs.com.pl
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