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[linux-lvm] Snapshot question...



Ok, now I have a question on how snapshots work...

I've read the following links:

http://tldp.org/HOWTO/LVM-HOWTO/snapshotintro.html

http://tldp.org/HOWTO/LVM-HOWTO/snapshots_backup.html

but am still unsure of something...

When a snapshot volume is created, it only needs to be large enough to accommodate any *changes* to the volume I'll be taking a snapshot of, correct? So, on a low volume mail server, 5GB should be way more than enough, especially if done in the middle of the night when it is essentially idling, right? I'm guessing that 500MB would probably be more than enough, but disk space is cheap, and I have plenty.

So, I have allocated 5GB of 'free space' in my volume group for snapshot use.

What I don't understand is... why am I mounting and then backing up the newly created snapshot volume, if it only contains the *changes* to the volume I really want to backup - which in my case is /var/virtual?

If the snapshot volume is only 5GB, how, by backing up *this* volume, am I backing up over 100GB of data that is in a different volume?

Tia for any responses,

--

Best regards,

Charles


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