[H-GEN] ext2 or ext3

[Tony Nugent]

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On Thu Jun 20 2002 at 11:06, Jason Henry Parker wrote:

> > An additional (handy) thing that you can do with the better journalled
> > filesystems is to have the ability of 'snapshots', or 'this is what the
> > filesystem looked like at previous point in time and this is the contents
> > of the files at that point in time'.  _Not_ an alternative to backups,
> 
> Also incredibly useful when you're trying to back up a busy filesystem
> while it's still active, *if* you have the storage to keep the changes
> and/or snapshot around long enough for the backup to be successful and
> keep the `real' filesystem useful for users, no?

I had no idea that ext3 could be used to do that.  (Very cool).

> I was thinking of using this sort of functionality to assist creating
> backup images for tape.

One of the features of LVM (logical volume manager) is that it
allows you to do exactly that... create filesystem "snapshots".

This is very useful for backups of files (especially large ones)
that are constantly changing (eg, sql databases, log files, or a
mail spool directory) -- just temporarily shutdown the sql server,
do the snapshot, restart the daemon and backup the snapshot (rather
than the live filesystem).

That way the server is only offline for a minimal time, and what you
backup is internally consistent rather than corrupted due to changes
made during the time it would take to put it all onto tape.

Do all journalling filesystems have this feature?

Cheers
Tony

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