[ClusterLabs] how to "switch on" cLVM ?

Digimer lists at alteeve.ca
Mon Jun 6 14:17:35 EDT 2016

On 06/06/16 01:13 PM, Lentes, Bernd wrote:
> Hi,
> i'm currently establishing a two node cluster. I have a FC SAN and two hosts. My services are integrated into virtual machines (kvm). The vm's should reside on the SAN.
> The hosts are connected to the SAN via FC HBA. Inside the hosts i see already the volume from the SAN. I'd like to store each vm in a dedicated logical volume (with or without filesystem in the LV).
> Hosts are SLES 11 SP4. LVM2 and LVM2-clvm is installed.
> How do i have to "switch on" clvm ? Is locking_type=3 in /etc/lvm/lvm.conf all which is necessary ?

That tells LVM to use cluster locking, you still need to actually
provide the cluster locking, called DLM. With the cluster formed (and
fencing working!), you should be able to start the clvmd daemon.

> In both nodes ?


> Restart of the init-scripts afterwards sufficient ?

No, DLM needs to be added to the cluster and be running.

> And how do i have to proceed afterwards ?
> My idea is:
> 1. Create a PV
> 2. Create a VG
> 3. Create several LV's

If the VG is created while dlm is running, it should automatically flag
the VG as clustered. If not, you will need to tell LVM that the VG is
clustered (-cy, iirc).

> And because of clvm i only have to do that on one host and the other host sees all automatically ?

Once clvmd is running, any changes made (lvcreate, delete, resize, etc)
will immediately appear on the other nodes.

> Later on it's possible that some vm's run on host 1 and some on host 2. Does clvm needs to be a ressource managed by the cluster manager ?

Yes, you can live-migrate as well. I do this all the time, except I use
DRBD instead of a SAN and RHEL instead of SUSE, but those are trivial
differences in this case.

> If i use a fs inside the lv, a "normal" fs like ext3 is sufficient, i think. But it has to be a cluster ressource, right ?

You can format a clustered LV with a cluster unaware filesystem just
fine. However, the FS is not made magically cluster aware... If you
mount it on two nodes, you will almost certainly corrupt the FS quickly.
If you want to mount an LV on two+ nodes at once, you need a
cluster-aware file system, life GFS2.

> Thanks in advance.
> Bernd

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