[Linux-cluster] CLVMD without GFS

[brem belguebli]

Hi all,

I think there is something to clarify about using CLVM across a cluster in a
active/passive mode without GFS.

>From my understanding, CLVM keeps LVM metadata coherent among the cluster
nodes and provides a cluster wide locking mechanism that can prevent any
node from trying to activate a volume group if it has been activated
exclusively (vgchange -a e VGXXX)  by another node (which needs to be up).

I have been playing with it to check this behaviour but it doesn't seem to
make what is expected.

I have 2 nodes (RHEL 5.3 X86_64, cluster installed and configured) , A and B
using a SAN shared storage.

I  have a LUN from this SAN seen by both nodes, pvcreate'd /dev/mpath/mpath0
, vgcreate'd vg10 and lvcreate'd lvol1 (on one node), created an ext3 FS on
/dev/vg10/lvol1

CLVM is running in debug mode (clvmd -d2 ) (but it complains about locking
disabled though locking set to 3 on both nodes)

On node A:

          vgchange -c y vg10 returns OK (vgs -->  vg10     1   1   0 wz--nc)

          vgchange -a e --> OK

          lvs returns lvol1   vg10   -wi-a-

On node B (while things are active on A, A is UP and member of the
cluster ):

          vgchange -a e --> Error locking on node B: Volume is busy on
another node
                                   1 logical volume(s) in volume group
"vg10" now active

 It activates vg10 even if it sees it busy on another node .

on B, lvs returns lvol1   vg10   -wi-a-

as well as on A.

I think the main problem comes from the fact that, as it is said when
starting CLVM in debug mode,  WARNING: Locking disabled. Be careful! This
could corrupt your metadata.

IMHO, the algorithm should be as follows:

VG is tagged as clustered (vgchange -c y VGXXX)

if a node (node P) tries to activate the VG exclusively (vgchange -a VGXXX)

ask the lock manager to check if VG is not already locked by another node
(node X)

if so, check if node X is up

if node X is down, return OK to node P

else

return NOK to node P (explicitely that VG is held exclusively by node X)

Brem

PS: this shouldn't be a problem with GFS or other clustered FS (OCFS,
etc...) as no node should try to activate exclusively any VG.
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