[Linux-cluster] CLVMD - Do I need it???

[Jonathan Brassow]

On Tue, 2006-09-12 at 10:04 -0400, Lon Hohberger wrote:
> On Tue, 2006-09-12 at 09:25 +0100, HAWKER, Dan wrote:
> > 
> > Hi All,
> > 
> > Have an EMC SAN unit on the way. I plan to use it as the central store for a
> > couple of servers setup as a cluster, using GFS. As the SAN unit can handle
> > all of its own Logical Volume management natively, I presume I don't have to
> > use/implement CLVMD and hence can cut one layer of complexity in the disk
> > structure away.
> 
> > Am I correct in this assumption, or does GFS/RHCS need to use CLVMD in its
> > configuration???
> 
> You don't need CLVM if you intend to use the internal array tools, but
> it's a "nice to have" thing.  After all, we've had GFS (and simple
> failover, for that matter) for a few years -- while CLVM is a relatively
> new technology.  Some SANs can do this internally too, of course.
> 
> For example, if you had CLVM and you add another array, I'm pretty sure
> you could use CLVM to extend an existing logical volume on to the second
> array while the cluster is running.


I think one of the big things is naming - ensuring that the device name
is always the same on all nodes in the cluster - regardless of any
devices added/changed/removed.  If you can do that, in addition to
storage management, then there is probably no need to involve LVM
(cluster or not).  If you plan to use LVM on top of the storage device,
then you must use clvmd.

 brassow