[CentOS-virt] Basic shared storage + KVM

Thu Jun 21 11:29:09 UTC 2012
Philip Durbin <philipdurbin at gmail.com>

To allow for live migration between hypervisors, I've been using NFS for shared storage of the disk images for each of my virtual machines.  Live migration works great, but I'm concerned about performance as I put more and more virtual machines on this infrastructure.  The Red Hat docs warn that NFS won't scale in this situation and that iSCSI is preferred.

I'm confused about how to effectively use iSCSI with KVM, however. libvirt can create new disk images all by itself in a storage pool backed by NFS, like I'm using, but libvirt can not create new disk images in a storage pool backed by iSCSI on its own.  One must manually create the LUN on the iSCSI storage each time one wants to provision a virtual machine.  I like how easy it is to deploy new virtual machines on NFS; I just define the system in Cobbler and kickstart it with koan.

I think my solution to the problem of how to scale shared storage may be OpenStack, which promises this as a feature of Swift.  Then, perhaps, I'll be able to leave NFS behind.

I'd be happy to hear more stories of how to scale shared storage while continuing to allow for live migration.


On Jun 19, 2012, at 5:50 PM, Andrea Chierici <andrea.chierici at cnaf.infn.it> wrote:

> Hi,
>>   Please help me understand why you are doing it this way?  I'm using
>> Xen with integrated storage, but I've been considering separating my
>> storage from my virtual hosts.  Conceptually, we can ignore the Xen/KVM
>> difference for this discussion.  I would imagine using LVM on the
>> storage server then setting the LVs up as iSCSI targets.  On the virtual
>> host, I imagine I would just configure the new device and hand it to my
>> VM.
> I am open to any suggestion. I am not really an expert of iscsi, so I 
> don't know what is the best way to implement a solution where a small 
> group of hv support live migration with a shared storage. This way 
> looked rather straightforward and for some level, documented on official 
> redhat manuals.
> The problem is that there is no mention about this LVM problem :(
> Initially I tried configuring the raw iscsi device ad storage pool but 
> virt-manager reported it was 100% occupied even if that was not true 
> (indeed 0% was occupied).
> Andrea
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