RE: [Xen-users] xen storage options - plase advise

[Jeff Sturm <jeff.sturm@xxxxxxxxxx>]

> -----Original Message-----
> So in general terms, how would I setup LVM (clvm)? Let's say I have
two
> servers (in this case running sles11). Each server has the SAME
> vdisk(LUN) from our Xiotech SAN assigned to it for storage. Let's say
> it's a 400gb vdisk. If I add additional servers, they too would be
> assigned the same vdisk. Similarly, I could add additional vdisks when
> more storage is required.

Each node in your cluster must be able to access the storage exported
from your SAN.

You'd create a CLVM much like an LVM.  First configure your cluster,
then create a volume group on the SAN-exported device.
Once created you'd start clvmd and run a "vgchange -c y" on the volume
group to promote it to a clustered volume group.

> Anyway, on the first server I setup LVM. Somehow the second server
would
> also see that as lvm and be able to mount it?

When a volume group is clustered, all nodes participating in your
cluster will see this volume group (e.g. in a "vgs" command) and any
changes in this volume group (creating/deleting logical volumes, etc.)
will be synchronized to all nodes in the cluster.

> I will search for some documentation on setting up clvm, but my
> questions are:
> 
> 1) Is this where I would/could use clvm?

We use it to carve out raw storage from our SAN and export logical
volumes to domU's as a block device.  This is a good use of CLVM.  You
can use it with a clustered file system (GFS) or by itself.

> 2) On each server would they see the logical volume at a mount point?

Each node would see each logical volume in the clustered volume group as
a block device.  That block device can be used raw, exported to a domU
(e.g. via phy:) or used for a filesystem.

A standard filesystem created within such a logical volume can only be
mounted on one node at a time.  To mount on multiple nodes at once, you
need a clustered filesystem to ensure file metadata is synchronized
amongst all cluster nodes.

> 3) Would I need to use xen's built in locking mechanisms or is there
> some builtin locking like ocfs2 has?

CLVM has its own locking protocol based on DLM.

-Jeff



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