[virt-tools-list] Live migration

[Phil Meyer]

  On 09/01/2010 05:59 PM, Mike Hall wrote:
> We've been working on the assumption that KVM live migration would require the use of a clustered filesystem such as GFS2.
>
> However this page from the Virtualization Guide appears to suggest that either iSCSI or NFS storage would also work:
>
> http://www.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5/html/Virtualization_Guide/chap-Virtualization-KVM_live_migration.html
>
> So is live migration of VMs on KVM possible using iSCSI or NFS storage without any type of clustered filesystem?
>

We have experimented a great deal on a project to use iscsi targets for 
each VM.  We script the live migrate process like this:

1. add the target host iscsi-initiator to the existing volume permissions
2. the target host logs into the existing iscsi volume
3. the target host adds an entry into /etc/multipath.conf
       we use multipath to enable persistent naming conventions for volumes
4. live-migrate
5. virsh dumpxml and virsh define xmlfile on the target host to enable 
reboots of VM
6. remove original host iscsi initiator from volume permissions
7. virsh undefine VM on original host
8. log out of iscsi volume on original host
9. remove /etc/multipath.conf entry from original host

Using iscsi targets for each VM has major performance implications over 
NFS and GFS2, depending on application and i/o load.

Our tests indicate a 10-100 times disk i/o performance improvement for 
our applications, and allow us a VM density of up to 60+ VMs per host!

With limited VMs it would not be necessary to do all the clean up.

Good Luck!