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Re: [Qemu-devel] Re: [PATCH 0/3 v4] Live migration without shared storag


From: Liran Schour
Subject: Re: [Qemu-devel] Re: [PATCH 0/3 v4] Live migration without shared storage
Date: Tue, 13 Oct 2009 10:14:16 +0200

address@hidden wrote on 12/10/2009
18:51:32:

> On 10/12/2009 06:09 PM, Michael Tokarev wrote:
> > address@hidden wrote:
> >> This series adds support for live migration without shared storage,
> >> means copy the storage while migrating. It was tested with KVM.
> >> Supports 2 ways to replicate the storage during migration:
> >> 1. Complete copy of storage to destination 2. Assuming the storage is
> >> cow based, copy only the allocated data, time of the migration will be
> >> linear with the amount of allocated data (user responsibility to
> >> verify that the same backend file reside on src and destination).
> >
> > Hmm. How about something like:
> >
> > migrate exec:"rsync file1 file2 ... remote: && nc remote port"
>
> That can surely work to copy the base files, but it is a task for an
> upper level like libvirt.  For qemu, copying the copy-on-write data is
> enough.
>

I agree that it can be useful to let an upper level component to copy the
storage
but you will need a way to synchronize with that layer: 1. qemu --> upper
layer:
vm suspended,no more writes to disk.
2. upper layer --> qemu: storage replication is done.
I don't see how without it you will have a valid copy of the storage.

However make use of the copy on write data and cut the amount of
transferred data
can be done only from inside qemu.

- Liran





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