Re: [Xen-devel] disks under migration

[Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>]

> How does live (or normal) migration handle the disks involved?
> Are they transfered, or does the xfrd keep some sort of channel open?

xend currently doesn't give you any help and do this
automatically, but its something we might add in the future.

For most of our VMs we either use NFS root to a central server,
or iscsi direct to a SAN, so there's no block device as such to
migrate.[*]

If you do want to access back to a local drive, then you'll need
to set this up yourself. There are a bunch of network block
device options available, all of which should work: iscsi, NBD,
ENBD, GNBD. 

We could add the equivalent of the vif-bridge script to xend for
block devices. This would provide simple hooks to enable the
block device export/import to be set up.  However, chances are
we'd want this to be stateful and smarter, so its probably best
to do a xend plugin rather than just use scripts. 
 
> And I assume a saved domain that is restored on another host must have
> all its disk and swap space transfered to the new host as well, correct?

Yep. No auto magic, not yet ;-)

Ian

[*] Even using iscsi, there are some situations where you'd
prefer to have the iscsi driver in domain 0 and export the disk
as a block device to other domains. For example, if you have a
hardware iscsi initiator in the machine. In this instance, you'd
prefer to move the iscsi disk as part of the migrate. 


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