[DRBD-user] Effect of writing directly to DRBD backing volume while offline?

Simon Carey-Smith clipclopnz at gmail.com
Sat May 31 20:07:36 CEST 2008

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

I have an LVM partition /dev/vg/lvdata being replicated by DRBD (drbd on top of
LVM2).  I use external metadata on a separate LVM partition of 256 MB.

I would like to know the effect of mounting and writing to the LVM partition
directly while DRBD is stopped.  I can't find anything mentioned in the
documentation about doing this.

I ask because when I tried this, after bringing DRBD back up everything seemed
fine, it replicated the changes to the secondary.  However, 2 days later I
started receiving messages in the system log like the following:

kernel: attempt to access beyond end of device
kernel: drbd0: rw=0, want 14,702,736,608 limit 579,141,632

After another few days DRBD crashed and fscking the LVM volume found loads of
problems (not surprising, as it was trying to write to a block value which is
about 25 times bigger than the maximum which exists!)

So, it is not possible to directly write to the LVM partition without screwing
up DRBD?
If I needed to do this, would this require running "drbdadm create-md r$"
afterwards on the primary and secondary?

Any ideas on how DRBD could be trying to write to a block which is so much out
of range?
Thanks, Simon

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