Re: [gentoo-user] Writing a bash script or thinking about it anyway.

["Jesús Guerrero" <i92guboj@terra.es>]

On Tue, 22 Dec 2009 16:51:08 +0200, Alan McKinnon
<alan.mckinnon@gmail.com>
wrote:
> On Tuesday 22 December 2009 16:21:08 Christian Könitzer wrote:
>> a question to b):
>> Can you tell me a fs that supports snappshots (I'm planing to set up a
>> new server so you can choose a new fs... (now I am using reiserfs)) and
>> maybe how to use it (link)? So if you say "or LSM" does this mean I can
>> achieve this also woth LVM? How?
>> thx...
> 
> None of the traditional filesystems (ext2|3, reiser) support snapshots.
> ZFS< 
> Btrfs do, possibly ext4 also (the last is a hunch only).

That's basically true. However btrfs is quite experimental still, and I
have no serious experience with ZFS, it kind of turns me back the fact that
it's a FUSE based fs, though it's certainly possible to use it even for a
root system provided that your kernel can load the module at bootup
(initrd), I have no idea if there's any downside. I don't have either any
notice about snapshotting in ext4 (I remember the plan being discussed but
I don't think it has been finally implemented, I'd like to be wrong on this
one though).

> LVM snapshots a volume, not the filesystem on it. So it tracks extents
> that 
> have changed, not individual files. For backup purposes though, volume
and
> fs 
> snapshots are equivalent.
> 
> Snapshots with LVM are easy as pie:
> 
> - create a new volume which is a snapshot of an existing one
> - mount the snapshot somewhere
> - copy,backup,etc as you like. The volume is read-only so you can't
break
> it
> - umount snapshot
> - destroy snapshot
> 
> The LVM man pages contain a wealth of data, as does Google and the LVM 
> documentation at redhat.com

Yep, just googling for something along the lines of "lvm snapshot backup"
should give you enough info to start researching. However, for this to be a
possibility you first need to convert your system to use lvm.

-- 
Jesús Guerrero