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Re: [Qemu-devel] [PATCH 2/5] migration: Create block capability
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH 2/5] migration: Create block capability |
Date: |
Tue, 16 May 2017 11:08:35 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0 |
On 05/16/2017 11:00 AM, Markus Armbruster wrote:
>>>> # periodic mode. (Since 2.8)
>>>> #
>>>> +# @block-incremental: enable block incremental migration (Since 2.10)
>>>> +#
>>>
>>> What's "block incremental migration" and why should I care?
>>
>> This is good, I will try.
>>
>> "block incremental migration assumes that we have a base image in both
>> sides, and then we continue writting in one of the sides. This way we
>> need to only migrate the changes since the previous state where it was
>> the same in both sides".
>>
>> I am not sure what to put there, really.
>
> Well, to suggest something, I'd first have to figure out WTF incremental
> block migration does. Your text helps me some, but not enough. What
> exactly is being migrated, and what exactly is assumed to be shared
> between source and destination?
>
> Block migration is scandalously underdocumented.
If I have:
base <- active
on the source, then:
block migration without incremental creates:
active
on the destination (the entire disk contents are migrated). Conversely,
block migration WITH incremental assumes that I have pre-created 'base'
on the destination (easy to do, since base is read-only so it can be
copied prior to starting the migration), and the migration results in:
base <- active
on the destination, where only the contents of active were transferred
by qemu.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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- [Qemu-devel] [PATCH v4 0/5] Remove old MigrationParams, Juan Quintela, 2017/05/16
- [Qemu-devel] [PATCH 1/5] hmp: Use visitor api for hmp_migrate_set_parameter(), Juan Quintela, 2017/05/16
- [Qemu-devel] [PATCH 5/5] block migration: Allow compile time disable, Juan Quintela, 2017/05/16
- [Qemu-devel] [PATCH 4/5] migration: Remove old MigrationParams, Juan Quintela, 2017/05/16
- [Qemu-devel] [PATCH 2/5] migration: Create block capability, Juan Quintela, 2017/05/16
- Re: [Qemu-devel] [PATCH 2/5] migration: Create block capability, Markus Armbruster, 2017/05/16
- Re: [Qemu-devel] [PATCH 2/5] migration: Create block capability, Juan Quintela, 2017/05/16
- Re: [Qemu-devel] [PATCH 2/5] migration: Create block capability, Markus Armbruster, 2017/05/16
- Re: [Qemu-devel] [PATCH 2/5] migration: Create block capability,
Eric Blake <=
- Re: [Qemu-devel] [PATCH 2/5] migration: Create block capability, Markus Armbruster, 2017/05/16
- Re: [Qemu-devel] [PATCH 2/5] migration: Create block capability, Eric Blake, 2017/05/16
- Re: [Qemu-devel] [PATCH 2/5] migration: Create block capability, Markus Armbruster, 2017/05/16
- Re: [Qemu-devel] [PATCH 2/5] migration: Create block capability, Juan Quintela, 2017/05/16
[Qemu-devel] [PATCH 3/5] migration: Remove use of old MigrationParams, Juan Quintela, 2017/05/16