Re: [Xen-users] Xen and GFS

[John Madden <jmadden@xxxxxxxxxxx>]

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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