[Pacemaker] KVM live migration and multipath

[Sven Arnold]

Thank you for replying, Vladislav!


> I think the problem should be unrelated to iSCSI, you have correct setup
> (of course I did not thoroughly look through all info, but idea is
> perfectly correct).

Thank you for confirming.

> Did you turn caching off for your VMs disks?

That's a point. Indeed caching was not explicitely turned off and I just 
noticed that the default setting of the cache attribute of the device 
tag in libvirt has changed. [1]
I would expect that libvirt flushes all caches before finalizing the 
migration process. But it is probably best to turn off caches anyway.

I have now configured:

<disk type='block' device='disk'>
       <driver name='qemu' type='raw' cache='none'/>
       <source dev='/dev/mapper/1p-lun1-vm_disk'/>
       <target dev='vda' bus='virtio'/>
       <address type='pci' domain='0x0000' bus='0x00' slot='0x04' 
function='0x0'/>
</disk>

Unfortunately the problem persists :-(
(To check i run a loop of dd commands while migrating the vm, 
restarting iscsi initiators and iscsitargets. I still get errors in the fs.)


>> I have configured iSCSI timeouts rather short (noop_out_timeout 5
>> seconds) and "no_path_retry queue" on the multipath device.
>>
>> My question(s):
>>
>> 1) Is it conceptually wrong what I am trying to accomplish?
>
> No, I use almost the same setup in production. Except I use IET and I
> have cLVM on top of luns.

Good to hear. Could the use of cLVM make a diffenrence (since this layer 
is cluster aware)?


>> 5) Is TGT multipath capable?
>
> Multipathing is much more an initiator concept, so I cannot see how
> target side may affect that (unless it has some serious flaws with
> reordering).

I think so also, but was a bit irritated that at the webpage of another 
implementation (istgt, [2]) it is explicitly mentioned that it is 
multipath capable.

Thanks for your help so far,

Sven

[1] http://libvirt.org/formatdomain.html#elementsDevices
[2] http://www.peach.ne.jp/archives/istgt/