Re: KVM, iSCSI and High Availability

[Avi Kivity <avi@redhat.com>]

On 03/25/2011 10:26 PM, Marcin M. Jessa wrote:
> Hi.
>
> Over the last several days I've been reading, asking questions, 
> searching the Internet to find a viable HA stack for Ubuntu with KVM 
> virtualization and shared iSCSI storage. And I'm nearly as confused as 
> when I started.
>
> Basically I'm trying to build a KVM enviroment with an iSCSI SAN and 
> I'm not quite sure what approach to use for storing the virtual guests.
> What I understand to get max speed I should install directly to iSCSI 
> exported raw devices instead of backing disks.
> I'm not sure creating many small LUNs, one for each of the guests is a 
> good idea.
> Would it be better to create just one big LUN and then use LVM to 
> devide it and assign one "chunk" for each of the guests?
> In the same setup I would also like to implement some kind of 
> automatic failover so if one of the KVM hosts is down I could 
> automatically move guests over to the other one. Or just perform live 
> migration and move one of the guest over to a different host with 
> spare capacity.
> What would be the best approach to implement a solution like that?
>

One LUN per image allows you to implement failover, LVM doesn't (but 
cluster-LVM does).  I recommend using one LUN per image; it's much simpler.

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