[ovirt-users] How long do your migrations last?

[Darrell Budic]

I’m under the impression it depends more on the hosts memory assignment than disk size. libvirt has to synchronize that over your networking setup. Your times sound like mine over 1G ethernet with a 9000 MTU, most of my machines are 1-4GB ram. I’ve another setup with a 10G backend that can migrate larger machines much faster. Things that do a lot of memory access (databases, say) or use more of their allocated memory, tend to take longer to migrate as it’s more work for libvirt to get it synchronized.

A 10G+ backend is the best way to speed this up, and there are libvirt variables you can tweak to allocate more bandwidth to a migration (and the # of simultaneous migrations you allow). I think the defaults are 3 at max of 30% of your available bandwidth. I don’t think this takes bonds into account, so if you have bonded connections, you may be able to allocate more % or allow more simultaneous migrations. Keep in mind that if you’re sharing bandwidth/media with iSCSI, that some bandwidth will be needed there as well, how much depends on your storage load. A dedicated NIC could definitely help, especially if you’re trying to tune libvirt for this.

  -Darrell

> On Feb 13, 2015, at 8:53 AM, Nicolas Ecarnot <nicolas at ecarnot.net> wrote:
> 
> Hello list,
> 
> Our storage domains are iSCSI on dedicated network, and when migrating VMs, the duration varies according to the size of the vDisks.
> 
> The smallest VMs are migrated in about 20 seconds, while the biggest one may take more than 5 or 10 minutes.
> The average duration is 90 seconds.
> 
> Questions :
> 
> 1- Though I may have understood that the task of migration was made by the SPM, I don't know what it actually does? (which bytes goes where)
> 
> 2- Do our times sound OK, or does it look like improvable?
> 
> 3- What bottleneck should I investigate? I'm thinking about the dedicated hardware NICs setup of the hosts, the SAN, the MTU has already been setup at 9000...
> 
> Any ideas welcomed.
> 
> -- 
> Nicolas Ecarnot
> _______________________________________________
> Users mailing list
> Users at ovirt.org
> http://lists.ovirt.org/mailman/listinfo/users