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RE: [Xen-users] Xen and GFS

I've done exactly this (with iSCSI instead of FC), but I did take the
extra step to configure GFS, as I intended each cluster node to run
various DomU's (3 or 4 on each).  The DomU VBD's are all stored on the
same iSCSI LUN, so each node can read/write to the LUN simultaneously
with GFS.

It took a lot of trial and error to get everything working - I got stuck
trying to figure out why the LVM2-cluster package was missing in Fedora
Core 5, and finally realized that it wasn't really necessary as long as
I did all of the LVM administration from one node and used the
pvscan/vgscan/lvscan tools on the other nodes to refresh the metadata.

Stephen Palmer
Gearbox Software
CIO/Director of GDS

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-users-
> bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of John Madden
> Sent: Tuesday, April 18, 2006 3:31 PM
> To: xen-users@xxxxxxxxxxxxxxxxxxx
> Cc: Jim Klein
> Subject: Re: [Xen-users] Xen and GFS
> On Tuesday 18 April 2006 16:17, Jim Klein wrote:
> > The setup I have is 3 - AMD_64DP server blades w/ 4Gb RAM each,
> > attached to FC SAN. The thought was that I would create a GFS volume
> > on the SAN, mount it under Xen dom0 on all 3 blades, create all the
> > VBDs for my VMs on the SAN, and thus be able to easily migrate VMs
> > from one blade to another, without any intermediary mounts and
> > unmounts on the blades. I thought it made a lot of sense, but maybe
> > my approach is wrong.
> Not necessarily wrong, but perhaps just an unnecessary layer.  If your
> intent
> is HA Xen, I would set it up like this:
> 1) Both machines connected to the SAN over FC
> 2) Both machines having visibility to the same SAN LUN(s)
> 3) Both machines running heartbeat with private interconnects
> 4) LVM lv's (from dom0) on the LUN(s) for carving up the storage for
> domU's
> 5) In the event of a node failure, the failback machine starts with
> an "/etc/init.d/lvm start" or equivalent to prep the lv's for use.
> xend
> start, etc.
> For migration, you'd be doing somewhat the same thing, only you'd need
> separate SAN LUN (still use LVM inside dom0) for each VBD.  My
> understanding
> is that writing is only done by one Xen stack at once (node 0 before
> migration, node 1 after migration, nothing in between), so all you
have to
> do
> is make that LUN available to the other Xen instance and you should be
> set.
> A cluster filesystem should only be used when more than one node must
> write
> to the same LUN at the same time.
> John
> --
> John Madden
> Sr. UNIX Systems Engineer
> Ivy Tech Community College of Indiana
> jmadden@xxxxxxxxxxx
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