[Linux-cluster] CLVMD without GFS

[Christine Caulfield]

Hiya,

I've just tried this on my cluster and it works fine.

What you need to remember is that lvcreate on one node will also 
activate the LV on all nodes in the cluster - it does an implicit 
lvchange -ay when you create it. What I can't explain is why vgchange 
-ae seemed to work fine on node A, it should give the same error as on 
node B because LVs are open shared on both nodes.

Its not clear to me when you tagged the VG as clustered, so that might 
be contributing to the problem. When I create a new VG on shared storage 
it automatically gets labelled clustered so I have never needed to do 
this explicitly. If you create a non-clustered VG you probably ought to 
deactivate it on all nodes first as it could mess up the locking 
otherwise. This *might* be the cause of your troubles.

The error on clvmd startup can be ignored. It's caused by clvmd ussing a 
background command with --no_locking so that it can check which LVs (if 
any) are already active and re-acquire locks for them

Sorry this isn't conclusive, The exact order in which things are 
happening is not clear to me.

Chrissie.

On 07/21/2009 10:21 AM, brem belguebli wrote:
> 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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