Re: [Xen-users] Xen and GFS

[Jim Klein <jklein@xxxxxxxxxxxxxxxx>]

Thanks again. I was trying to avoid the mount/unmount complexity and  
use SAN space more efficiently by simply keeping all the xenU domains  
on the shared file system, but it looks as though that won't work  
quite like I had hoped. I'm not looking for HA per se (although this  
is important,) more for flexibility when load balancing the VMs  
running on all the blades, and safer live migrations from blade to  
blade. I'm a little nervous about having a LUN up on two boxes at the  
same time, as I've got some experience with killing file systems this  
way (in the test lab, anyway.)

On Apr 18, 2006, at 1:30 PM, John Madden wrote:

> 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 the
> 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.   
> Then xend
> start, etc.
>
> For migration, you'd be doing somewhat the same thing, only you'd  
> need a
> 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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