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Re: [RFC qemu 0/6] mirror: implement incremental and bitmap modes
From: |
Max Reitz |
Subject: |
Re: [RFC qemu 0/6] mirror: implement incremental and bitmap modes |
Date: |
Thu, 3 Sep 2020 13:04:54 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 |
On 03.09.20 12:13, Fabian Grünbichler wrote:
> On August 21, 2020 3:03 pm, Max Reitz wrote:
>> On 18.02.20 11:07, Fabian Grünbichler wrote:
>>
>> [Sorry :/]
>
> same, I've been meaning to ping/pick this back up but other stuff got in
> the way. so thanks for the reminder to get this upstream ;)
>
>>
>>> picking up on John's in-progress patch series from last summer, this is
>>> a stab at rebasing and adding test cases for the low-hanging fruits:
>>>
>>> - bitmap mirror mode with always/on-success/never bitmap sync mode
>>> - incremental mirror mode as sugar for bitmap + on-success
>>>
>>> Fabian Grünbichler (4):
>>> mirror: add check for bitmap-mode without bitmap
>>> mirror: switch to bdrv_dirty_bitmap_merge_internal
>>> iotests: add test for bitmap mirror
>>> mirror: move some checks to QMP
>>>
>>> John Snow (2):
>>> drive-mirror: add support for sync=bitmap mode=never
>>> drive-mirror: add support for conditional and always bitmap sync modes
>>
>> Looks reasonable to me. I would indeed merge patches 2 through 4 into a
>> single one, and perhaps switch patches 5 and 6.
>>
>> Also, we still need an S-o-b from John on patch 2.
>>
>> I have one question: When the mirror job completes successfully (or is
>> cancelled “successfully”), the bitmap is always fully cleared when the
>> job completes, right? (Unless in “never” mode.)
>
> I have to take a closer look as well, it's been a while ;)
No problem, I’m... *cough* not exactly in a hurry.
> IIRC the idea
> was that failed mirrors would allow re-using the bitmap for a next
> attempt, unless the mode is always. we are not using that feature (yet)
> though (see below).
>
>> Not that I think we should change the current implementation of “clear
>> sync_bitmap; merge dirty_bitmap into sync_bitmap;”. Just a question for
>> understanding.
>>
>>
>> Soo... What’s the plan?
>
> I'll rebase, squash as suggested and resend next week!
OK :)
> I am not sure how
> the S-O-B by John is supposed to enter the mix - should I just include
> it in the squashed patch (which would be partly authored, but
> not-yet-signed-off by him otherwise?)?
I’m not too sure on the proceedings, actually. I think it should be
fine if you put his S-o-b there, as long as your patch is somehow based
on a patch that he sent earlier with his S-o-b underneath. But I’m not
sure.
> do you pick it up once he's replied with one?
Yes, that’s what would be best.
> FWIW, with been running with this for quite a while downstream with no
> issues, but we are only using the following part:
>
> - create bitmap(s)
> - (incrementally) replicate storage volume(s) out of band (using ZFS)
> - incrementally drive mirror as part of a live migration of VM
> - drop bitmap(s)
>
> so no fancy semi-permanent bitmap that gets re-used here. I've been
> toying with implementing some sort of generic replication feature akin
> to zfs send/recv though, but given that we only have built-in persistent
> bitmaps with qcow2 and the chance of some other tool or the user messing
> up other image formats is high, the safe usage scenarios are a bit
> limited.
OK.
> we do use such long-running bitmaps for our new backup driver though,
> and it works quite well there!
Good! :)
Max
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- Re: [RFC qemu 0/6] mirror: implement incremental and bitmap modes, Fabian Grünbichler, 2020/09/03
- Re: [RFC qemu 0/6] mirror: implement incremental and bitmap modes,
Max Reitz <=
- Re: [RFC qemu 0/6] mirror: implement incremental and bitmap modes, Kevin Wolf, 2020/09/03
- Re: [RFC qemu 0/6] mirror: implement incremental and bitmap modes, Max Reitz, 2020/09/03
- Re: [RFC qemu 0/6] mirror: implement incremental and bitmap modes, Kevin Wolf, 2020/09/03
- Re: [RFC qemu 0/6] mirror: implement incremental and bitmap modes, Fabian Grünbichler, 2020/09/03
- Re: [RFC qemu 0/6] mirror: implement incremental and bitmap modes, Kevin Wolf, 2020/09/03
- Re: [RFC qemu 0/6] mirror: implement incremental and bitmap modes, Max Reitz, 2020/09/03