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[Linux-cluster] shared disk with virsh migration



Hi all,

I'm trying to decide whether I really need a cluster implementation to do what I want to do and I figured I'd solicit opinions. Essentially I want to have two machines running as virtualization hosts with libvirt/kvm. I have shared iSCSI storage available to both hosts and have to decide how to configure the storage for use with libvirt. Right now I see three possibilities:
1.  Setting an iSCSI storage pool in libvirt
	Pros:   Migration seems painless, including live migration
	Cons:   Need to pre-allocate LUNs on iSCSI box.
		Does not seem to take advantage of iSCSI offloading or multipathing
2.  Setting up a two-node cluster and running CLVM
	Pros:   Very flexible storage management (is snapshotting supported yet in clvm?)
		Automatic failover
	Cons:	Cluster infrastructure adds complexity, more potential for bugs
		Possible split brain issues?
3.  A single iSCSI block device with partitions for each VM mounted on both hosts
	Pros:	Easy migration, setup
	Cons:	Two hosts accessing the same block device outside of a
		cluster seems like it might lead to disaster

Right now I actually like option 3 but I'm wondering if I really am asking for trouble accessing a block device simultaneously on two hosts without a clustering infrastructure. I did this a while back with a shared-SCSI box and it seemed to work. I would never be accessing the same partition on both hosts and I understand that all partitioning has to be done while the other host is off, but is there something else I'm missing here?

Also, are people out there running option 2? Does it make sesne to set up a cluster as small as 2-nodes for HA virtualization or do I really need more nodes for it to be worthwhile? I do have all the fencing infrastructure I might need (PDUs and Dracs).

any help would be appreciated.  thanks
-alan


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