Re: [Qemu-devel] [PATCH] block-migration: deprecate block migration for the 1.2 release

[Stefan Hajnoczi]

On Wed, Aug 15, 2012 at 10:12:42AM +0200, Ruben Kerkhof wrote:
> On Tue, Aug 14, 2012 at 4:42 PM, Stefan Hajnoczi
> <address@hidden> wrote:
> > On Tue, Aug 14, 2012 at 08:32:31AM -0500, Anthony Liguori wrote:
> >> To be replaced with live block copy.
> >>
> >> Signed-off-by: Anthony Liguori <address@hidden>
> >> ---
> >>  migration.c |    9 +++++++++
> >>  1 files changed, 9 insertions(+), 0 deletions(-)
> >>
> >> diff --git a/migration.c b/migration.c
> >> index 653a3c1..babccf4 100644
> >> --- a/migration.c
> >> +++ b/migration.c
> >> @@ -482,10 +482,19 @@ void qmp_migrate(const char *uri, bool has_blk, bool 
> >> blk,
> >>      MigrationParams params;
> >>      const char *p;
> >>      int ret;
> >> +    static bool suppress_deprecation_message;
> >>
> >>      params.blk = blk;
> >>      params.shared = inc;
> >>
> >> +    if (blk && !suppress_deprecation_message) {
> >> +        qerror_report(ERROR_CLASS_GENERIC_ERROR,
> >
> > qerror_report_once() would be nice :).
> >
> >> +                      "Block migration is deprecated.  "
> >> +                      "See http://wiki.qemu.org/Features/LiveBlockCopy "
> >
> > The page doesn't exist, I think it should be:
> > http://wiki.qemu.org/Features/LiveBlockMigration
> 
> Can the new live block copy method still use tcp just like the current
> block migration? The wiki page only mentions iscsi.
> I make extensive use of block migration over tcp, which works fine and
> is handled by libvirt. I'd rather not introduce iscsi in my
> environment.

The new live block copy approach is different and that's why classic
block migration is only deprecated but not dropped:

Live block copy doesn't transfer data in-band during live migration.
Instead it currently requires storage access from both hosts, for
example:
1. NFS or CIFS
2. iSCSI or NBD

I think when classic block migration is removed for good it should be
just as easy to use through libvirt using TCP because that's still a
valid use case and probably the simplest one to get started.  (Libvirt
could orchestrate an NBD connection behind the scenes, for example.)

Stefan