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

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

[Michael Tokarev]

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).

Hmm. How about something like:

  migrate exec:"rsync file1 file2 ... remote: && nc remote port"

?

/mjt

[Qemu-devel] [PATCH 0/3 v4] Live migration without shared storage

[lirans]

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).

The code is being used by the Reservoir project: http://www.reservoir-fp7.eu/

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.

These patches addresses all previous comments.

Signed-off-by: Liran Schour <lirans@il.ibm.com>
---
 Makefile          |    1 +
 block-migration.c |  624 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 block-migration.h |   30 +++
 block.c           |   27 +++
 block.h           |    6 +-
 block_int.h       |    1 +
 buffered_file.c   |   10 +-
 hw/hw.h           |    9 +-
 migration-exec.c  |    9 +-
 migration-fd.c    |    7 +-
 migration-tcp.c   |    7 +-
 migration-unix.c  |    7 +-
 migration.c       |   21 ++-
 migration.h       |   20 ++-
 monitor.c         |   38 +++-
 qemu-monitor.hx   |   13 +-
 savevm.c          |   62 ++++--
 sysemu.h          |    2 +-
 vl.c              |    6 +-
 19 files changed, 851 insertions(+), 49 deletions(-)

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

[Paolo Bonzini]

On 10/12/2009 06:09 PM, Michael Tokarev wrote:
> 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).
>
> 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.

Paolo

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

[Liran Schour]

qemu-devel-bounces+lirans=il.ibm.com@nongnu.org wrote on 12/10/2009
18:51:32:

> On 10/12/2009 06:09 PM, Michael Tokarev wrote:
> > 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).
> >
> > 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

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

[Paolo Bonzini]

>>> 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.

Yes, I understand the reason for this feature.  What I meant was that 
you could use rsync to copy the base files from an upper level 
component, before the actual migration is started and qemu transfers the 
copy-on-write data live.

If Michael was saying instead "why is this needed at all", then you 
answered him.

Paolo