[Discuss] Backing up LVM partitions using snapshots

[markw at mohawksoft.com (markw at mohawksoft.com)]

> Pretty much everything Ed wrote is a good summation of the previous
> discussion.  To summarize the summary: LVM2 volumes are volatile.  If you
> are not very careful about this volatility then you could screw yourself
> over and you won't know it.  And even if you are so careful you can still
> end up screwed.

How?

>
> There is one particular case of this that makes me worry: loss or
> corruption of an incremental backup.  Because you are backing up the block
> device underneath you are backing up the raw blocks containing the file
> system metadata.  If you lose an incremental backup in the middle of your
> cycle then attempting to restore subsequent incrementals will leave that
> metadata in an inconsistent, possibly irrecoverable state.  In a worst
> case, loss of one incremental can result in the loss of almost an entire
> backup cycle's worth of work.

That can happen in a poorly designed system, sure. A file system
"incremental" backup is merely an optimization. A full "image" of the
source should be effectively backed up. By using the immediately previous
backup as a source for the full backup, you can record the data for the
full backup.

At any point in time, you should be able to restore a "whole" in one
operation. at any point in time, if you have a failed incremental, a full
backup restores the state.

>
> --Rich P.
>
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