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From: Peter Krempa <pkrempa@redhat.com>
To: Kevin Wolf <kwolf@redhat.com>
Cc: "Daniel P. Berrangé" <berrange@redhat.com>,
	qemu-block@nongnu.org, "Juan Quintela" <quintela@redhat.com>,
	qemu-devel@nongnu.org, "Markus Armbruster" <armbru@redhat.com>,
	"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
	"Max Reitz" <mreitz@redhat.com>,
	"Pavel Dovgalyuk" <pavel.dovgaluk@ispras.ru>,
	"Paolo Bonzini" <pbonzini@redhat.com>
Subject: Re: [PATCH 2/6] migration: introduce savevm, loadvm, delvm QMP commands
Date: Tue, 7 Jul 2020 08:38:53 +0200	[thread overview]
Message-ID: <20200707063853.GA9048@angien.pipo.sk> (raw)
In-Reply-To: <20200706161555.GE5052@linux.fritz.box>

On Mon, Jul 06, 2020 at 18:15:55 +0200, Kevin Wolf wrote:
> Am 03.07.2020 um 18:02 hat Daniel P. Berrangé geschrieben:
> > On Fri, Jul 03, 2020 at 04:49:33PM +0100, Dr. David Alan Gilbert wrote:
> > > * Daniel P. Berrangé (berrange@redhat.com) wrote:
> > > > On Thu, Jul 02, 2020 at 01:12:52PM -0500, Eric Blake wrote:
> > > > > On 7/2/20 12:57 PM, Daniel P. Berrangé wrote:

[...]

> > migration only does vmstate, not disks. The current blockdev commands
> > are all related to external snapshots, nothing for internal snapshots
> > AFAIK. So we still need commands to load/save internal snapshots of
> > the disk data in the qcow2 files.
> > 
> > So we could look at loadvm/savevm conceptually as a syntax sugar above
> > a migration transport that targets disk images, and blockdev QMP command
> > that can do internal snapshots. Neither of these exist though and feel
> > like a significantly larger amount of work than using existing functionality
> > that is currently working.
> 
> There is blockdev-snapshot-internal-sync, which does a disk-only
> snapshot of a single node. A snapshot of multiple nodes can be taken by
> putting multiple blockdev-snapshot-internal-sync inside a 'transaction'
> command.

Libvirt never implemented support for disk-only internal snapshots as I
didn't think they are worth it. We also made a mistake by using the
VIR_DOMAIN_SNAPSHOT_DISK_ONLY to switch to an external snapshot, so
while the XML can modify the snapshot to be internal it's not very clear
nor user-friendly to force an internal disk only snapshot.

> If we want to build on top of this, we'd have to implement a
> transactionable command for storing only the VM state to a specific
> node. This would probably still be a long-running job.

IMO we really want this also for external snapshots. Driving the
migration as standard migration is really suboptimal especially when the
user wants minimal downtime. Transactioning a post-copy style copy-on
write migration would simplify this a lot. I agree though that this is
for a different conversation.



  reply	other threads:[~2020-07-07  6:40 UTC|newest]

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-02 17:57 [PATCH 0/6] migration: bring savevm/loadvm/delvm over to QMP Daniel P. Berrangé
2020-07-02 17:57 ` [PATCH 1/6] migration: improve error reporting of block driver state name Daniel P. Berrangé
2020-07-02 18:36   ` Eric Blake
2020-07-02 19:13     ` Dr. David Alan Gilbert
2020-07-02 17:57 ` [PATCH 2/6] migration: introduce savevm, loadvm, delvm QMP commands Daniel P. Berrangé
2020-07-02 18:12   ` Eric Blake
2020-07-02 18:24     ` Daniel P. Berrangé
2020-07-03 15:49       ` Dr. David Alan Gilbert
2020-07-03 16:02         ` Daniel P. Berrangé
2020-07-03 16:10           ` Dr. David Alan Gilbert
2020-07-03 16:16             ` Daniel P. Berrangé
2020-07-03 16:22               ` Dr. David Alan Gilbert
2020-07-03 16:49                 ` Daniel P. Berrangé
2020-07-03 17:00                   ` Dr. David Alan Gilbert
2020-07-03 17:10                     ` Daniel P. Berrangé
2020-07-03 17:26                       ` Dr. David Alan Gilbert
2020-07-03 16:24             ` Peter Krempa
2020-07-03 16:26               ` Dr. David Alan Gilbert
2020-07-06 16:15           ` Kevin Wolf
2020-07-07  6:38             ` Peter Krempa [this message]
2020-07-07 10:33               ` Kevin Wolf
2020-07-07 10:41                 ` Peter Krempa
2020-07-03 17:22   ` Denis V. Lunev
2020-07-02 17:57 ` [PATCH 3/6] block: add ability to filter out blockdevs during snapshot Daniel P. Berrangé
2020-07-02 17:57 ` [PATCH 4/6] block: allow specifying name of block device for vmstate storage Daniel P. Berrangé
2020-07-02 17:57 ` [PATCH 5/6] migration: support excluding block devs in QMP snapshot commands Daniel P. Berrangé
2020-07-06 15:57   ` Kevin Wolf
2020-07-07  9:14     ` Daniel P. Berrangé
2020-07-07 10:11       ` Kevin Wolf
2020-07-02 17:57 ` [PATCH 6/6] migration: support picking vmstate disk " Daniel P. Berrangé
2020-07-02 18:19   ` Eric Blake
2020-07-03  8:37     ` Daniel P. Berrangé
2020-07-02 18:53 ` [PATCH 0/6] migration: bring savevm/loadvm/delvm over to QMP no-reply
2020-07-02 19:07 ` no-reply
2020-07-03 17:15 ` Denis V. Lunev
2020-07-03 17:22   ` Daniel P. Berrangé
2020-07-03 17:29     ` Denis V. Lunev
2020-07-06 14:28       ` Daniel P. Berrangé
2020-07-06 16:07         ` Denis V. Lunev
2020-07-06 15:27       ` Kevin Wolf
2020-07-06 15:29         ` Daniel P. Berrangé
2020-07-06 15:50           ` Kevin Wolf
2020-07-06 16:03             ` Daniel P. Berrangé
2020-07-06 16:10               ` Denis V. Lunev
2020-07-06 16:15                 ` Daniel P. Berrangé
2020-07-06 16:21               ` Kevin Wolf
2020-07-07  9:07                 ` Daniel P. Berrangé

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