[dm-crypt] Protection against data failure

Marc Ballarin ballarin.marc at gmx.de
Sat Aug 13 13:51:53 CEST 2011

On Wed, 10 Aug 2011 14:44:38 +0200
Sun_Blood <sblood at gmail.com> wrote:

> ...
> A final question that is more LVM but it sounds like you have some
> knowledge in this area. My setup is LVM -> LUKS -> Filesystem.
> If I use LVM snappshots on the LVM will the LUKS header also be
> backuped because it's on top of LVM?

That depends.

As an example:
Let's assume that /dev/mapper/sda is a linear mapping of /dev/sda.

cat /dev/zero > /dev/mapper/sda: snapshotting could preserve overwritten data
cat /dev/zero > /dev/sda: you are bypassing device mapper and overwritting
"form below" device mapper. So it can't do anything.

Snapshotting does not create physical copies of the snapshotted volume
automatically! Data will only be copied, if it is modified "from above" in
the original volume.

So, snapshotting is a very bad way to protect against accidental header
corruption and other forms of damage in lower levels. In general, snapshots
are no replacement for backups but can be a powerful addition.


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