[DRBD-user] Problem mounting lvm snapshot

Bart Coninckx bart.coninckx at telenet.be
Wed Oct 27 09:20:55 CEST 2010

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

On Tuesday 26 October 2010 23:20:40 Lewis Donzis wrote:
> We'd like to be able to make backups from our DRBD secondary by mounting
> the underlying filesystems.  After some searching, this appears to be a
> relatively common discussion: running DRBD on top of LVM, making a
> snapshow of the backing LV on the secondary, and mounting the snapshot LV.
> As has been discussed, it's not perfect, but it should produce reasonable
> results most of the time, at least no worse than if there had been a power
> failure.
> So, I'm sorry if this is a silly question, but I can't seem to get this to
> work.  It appears that DRBD permanently prevents mounting the backing
> device (or its snapshot) because "drbdadm create-md" function modifies the
> filesystem so that it can no longer be mounted except via the /dev/drbdX
> device.  In particular, attempting to mount a snapshot, or detaching DRBD
> from the backing device and attempting to mount the file system, or even
> just attempting to mount the backing device after create-md has run,
> results in:
>    mount: unknown filesystem type 'drbd'
> I see that the general concensus is that "it should work fine", so it
> seems like there must be some simple explanation.  Fyi,we're using Ubuntu
> 10.04 which loads DRBD version 8.3.7.
> Thanks for your assistance,
> lew
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You need to run LVM on top of DRBD for that. You can have LVM - DRBD - LVM, 
but the snapshotting should occur on the top LVM.


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