[Linux-cluster] LVM2 Cluster - How do it work ?

[Lon Hohberger]

On Wed, 2008-03-26 at 16:18 -0300, Davi Baldin wrote:
> Hello All,
> 
>  
> 
> I think to try using LVM2 in my clusters servers and have some questions
> about it. Something I got on google, but something not:
> 
>  
> 
> 1. Cluster-LVM is stable for production in Red Hat 5.1?

Always run the latest errata, but yes.

> 2. In my storage, when I create new LUN (two or more for performance)
> and create the new VG with LUNs as PV, the new VG it's visible for each
> node simultaneously? I can create three LV and mount one LV in one node,
> and mount two LVs in other node for this VG?


> 3. If I need quorum disk (for 3 nodes cluster), I can use a LV for the
> quorum disk?

(a) I'm not sure you'd need it in a 3-node case.  2/3 nodes crashing at
the same time

(b) It won't work very easily with clvm; you'd want to use shared raw
SCSI devices.  There's a circular dependency when using clvmd with
qdiskd:

  * qdiskd requires clvmd
  * clvmd requires cluster quorum
  * cluster quorum requires qdiskd

Historically, the solution has been one of two things:

  * don't use LVM for quorum partitions
  * If you must (which I doubt) use LVM for quorum partitions, you must
then also have all nodes in the cluster online.  At that point, you must
manually start qdiskd.


> 4. The LV mount occurs without any "know issue" in the node when the
> other node dies?

Clustered LVM protects the LVM metadata.  After a node dies, you will
not be able to mess with the LVM metadata on clustered VGs until fencing
completes.


> 5. The node shutdown dismount all LVs and the cluster can mount
> perfectly de LVs in other node?

Yes (as long as the remaining cluster has a quorum).


> 6. I can use the pv, vg and lv operations like an unclustered LVM2
> system?

Yes, after you set the locking type correctly in /etc/lvm/lvm.conf

-- Lon