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

[Avi Kivity <avi@redhat.com>]

On 11/02/2009 03:40 PM, lirans@il.ibm.com 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).
>
> 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.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.