[DRBD-user] Problem mounting lvm snapshot

Lewis Donzis lew at pt.net
Tue Oct 26 23:20:40 CEST 2010


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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