[plug] Backups

[Craig Ringer]

James Devenish wrote:
> In message <410623A2.2060604 at postnewspapers.com.au>
> on Tue, Jul 27, 2004 at 05:42:58PM +0800, Craig Ringer wrote:
> 
>>James: is `dump` capable of dumping a consistent point-in-time copy of
>>a filesystem that's in read/write use, or must measures like read-only
>>remounts or LVM snapshots be used?
> 
> 
> "Must"? I wouldn't say so. I don't think it is any worse than tar (i.e.
> won't lead to "filesystem corruption" as such).

The dump man page, which I've now had a look through, suggests that 
it'll deal OK with the FS changing under it, and you'll get a backup 
that can be restored. Whether it's a valid backup as far as the 
applications are concerned is another matter entirely - I wouldn't want 
to rely on this for backing up my mail spools, for example.

As you say, it looks like it's much the same as using tar on a live 
filesystem - I'm not game to do it, but for some things - or on less 
active servers - it could be OK.

I'm beginning to find the idea of using dump's differential backup 
support, combined with LVM snapshots, quite attractive. Alas, I'm using 
reiserfs on almost all my volumes because of the dynamic resizing and 
general lvm-friendlyness, and it doesn't seem to have a `dump` program.

> This remark is based
> entirely on personal fortune with dump/restore systems appearing to be
> robust. But I don't know whether this is by design or luck. Also, I
> don't know how reliable the ext2/3 dump/restore utilities are -- but I
> assume they're of high quality.

I think it's safe to assume they're well tested - but they seem to be 
going out of fashion, so I wonder how well that'll last.

--
Craig Ringer