LVM, SL7 and physical volume device names

The use of traditional /dev/sd[xx] disk device names has become increasingly unsafe in recent Linux installs. This is particularly so in an environment with SAN devices. For a while now, we have been mounting disk partitions by UUID, but until recently the LVM component has continued to rely on /dev/sd[xx] names.

The LVM component, on configure(), checks to see whether any additional physical volumes have been configured for a volume group. It does this by using the ‘pvs’ component to enumerate the physical volumes are associated with each volume group. The command vgextend (or vgcreate) are used to add a physical volume to a volume group. Unfortunately, these commands store away the resulting /dev/sd[xx] name of they physical volumes – and not the /dev/by-uuid name. This means that on subsequent reboots, there’s a high chance that the /dev/sd[xx] name will be wrong for a physical volume.

The solution is to generate a UUID on each physical volume (based on a hash of the physical path name), label the physical volume with that UUID (with pvcreate) and look for that UUID using ‘pvs -o pv_uuid,vg_name’ instead of looking for the /dev/sd[xx] device.