[DRBD-user] Problem mounting lvm snapshot

Felix Frank ff at mpexnet.de
Wed Oct 27 09:13:55 CEST 2010


On 10/26/2010 11:20 PM, 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'

Hi,

what are the options you try and mount the snapshot?

mount should not assume a "drbd" filesystem type. You probably use bad
options or have a faulty fstab. If all else fails, use
mount -t <correct_fs>.

Also, your filesystem should have been created after create-md, on the
/dev/drbdX device (unless I'm gravely mistaken). In any case, the fs has
no notion of DRBD whatsoever, as DRBD works on the block layer of things.

HTH,
Felix


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