Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
After a couple of days of struggling I got to the point where I have to
conclude that using LVM reliably over DRBD devices is impossible.
As there are many users using LVM on DRBD, I would like to be corrected,
of course.
Below, a step-by-step configuration of DRBD and LVM:
1. A relevant part of drbd.conf - our drbd0 device is on /dev/sda:
on san2 {
device /dev/drbd0;
disk /dev/sdb;
address 192.168.111.158:7789;
meta-disk internal;
}
2. Create drbd0 meta data:
# drbdadm create-md r0
3. Start DRBD:
# /etc/init.d/drbd start
4. Initial device sync:
# drbdadm -- --overwrite-data-of-peer primary all
5. Now, we should be able to create LVM - pvcreate first:
# pvcreate /dev/drbd0
Physical volume "/dev/drbd0" successfully created
6. Let's create a volume group - Houston, we have a problem!
# vgcreate testvolume /dev/drbd0
Found duplicate PV YIoJ98OFL3vhqhi7ek98UWkT7aBIzgrz: using /dev/sdb
not /dev/drbd0
Found duplicate PV YIoJ98OFL3vhqhi7ek98UWkT7aBIzgrz: using /dev/drbd0
not /dev/sdb
Found duplicate PV YIoJ98OFL3vhqhi7ek98UWkT7aBIzgrz: using /dev/sdb
not /dev/drbd0
Found duplicate PV YIoJ98OFL3vhqhi7ek98UWkT7aBIzgrz: using /dev/drbd0
not /dev/sdb
Volume group "testvolume" successfully created
7. pvs confirms it - LVM sits on /dev/sdb, not on /dev/drbd0 -
certainly, nothing will be replicated by DRBD:
# pvs
Found duplicate PV YIoJ98OFL3vhqhi7ek98UWkT7aBIzgrz: using /dev/sdb
not /dev/drbd0
PV VG Fmt Attr PSize PFree
/dev/sdb testvolume lvm2 a- 558.57G 558.57G
As device names are not necessarily persistent (if /dev/sdb is a iSCSI
drive, next time one boots it can be /dev/sdc) and a similar is for
device mapper devices (think of crypted devices), setting up filters in
lvm.conf will not be reliable.
How can I use LVM over DRBD devices *reliably*?
--
Tomasz Chmielewski
http://wpkg.org