Re: [Xen-devel] [PATCH] Add dm-userspace to the Xen kernel

[Dan Smith <danms@xxxxxxxxxx>]

NT> My question was, would this allow me to export a logical disk
NT> without having all the data present locally. The scenario I am
NT> thinking of would be applicable for VM migration across WANs.

Sure.

NT> In that case, if I was to represent a virtual disk as a number of
NT> logical blocks, I could have the userspace application page the
NT> logical blocks in on demand. This would be useful when a VM
NT> migrates to a machine it has never been to earlier. Does this make
NT> sense? Would it work with dm-userspace?

Definitely!  You could migrate the domain to another machine, and then
start a background process that starts copying its blocks to the other
machine.  If a request comes in for a block (dm-userspace will let you
handle it from the userspace app doing the copy), you immediately pull
it across to satisfy the request.  This would be a very interesting
way to support migration of domains with block devices, without
needing to wait for the block migration before starting the domain
back up on the target machine.

Very cool idea!

-- 
Dan Smith
IBM Linux Technology Center
Open Hypervisor Team
email: danms@xxxxxxxxxx

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