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Re: [Qemu-devel] [PATCH 0/3 v5] Live migration without shared storage

From: Liran Schour
Subject: Re: [Qemu-devel] [PATCH 0/3 v5] Live migration without shared storage
Date: Tue, 3 Nov 2009 11:40:55 +0200

- Liran

Avi Kivity <address@hidden> wrote on 02/11/2009 20:47:34:
> On 11/02/2009 03:40 PM, address@hidden wrote:
> > This series adds support for live migration without shared storage,
> > copy the storage while migrating. It was tested with KVM. Supports 2
> > 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).
> >
> > Live migration will work as follows:
> > (qemu) migrate -d tcp:0:4444 # for ordinary live migration
> > (qemu) migrate -d blk tcp:0:4444 # for live migration with
> complete storage copy
> > (qemu) migrate -d blk inc tcp:0:4444 # for live migration with
> incremental storage copy, storage is cow based.
> >
> I'd like to see the syntax generalized.  For one, the guest may have
> several disks; an install image cdrom might be available as an nfs image
> but the main storage is local.  Secondly, there can be several levels of
> cow and we want to control which one we copy.
> I'll leave the exact details to the qpeople, but if we can specify a
> copy depth for each device, where 0=copy nothing, n=copy everything,
> 1=copy the last level (equivalent to -d blk inc) I think we'll have
> covered everything.

I propose the following syntax:
migrate [-d] [-b [<device:copy_level> ...<device:copy_level>]]
Where device will be the name of the device: ide0-hd0. And copy_level will
be integer or n, 0=flat copy of the device, 1=copy the last level ...
n=copy all levels.
All HD devices that will not appear in the command will be treated as
copy_level=0. All devices != BDRV_TYPE_HD will be ignored.

What do you think?

- Liran

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