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Re: [Qemu-block] [PATCH] blockdev-backup: enable non-root nodes for back
From: |
Max Reitz |
Subject: |
Re: [Qemu-block] [PATCH] blockdev-backup: enable non-root nodes for backup |
Date: |
Mon, 4 Dec 2017 23:21:10 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 |
On 2017-12-04 23:15, John Snow wrote:
>
>
> On 12/01/2017 02:41 PM, Max Reitz wrote:
>> ((By the way, I don't suppose that's how it should work... But I don't
>> suppose that we want propagation of dirtying towards the BDS roots, do
>> we? :-/))
>
> I have never really satisfactorily explained to myself what bitmaps on
> intermediate notes truly represent or mean.
>
> The simple case is "This layer itself serviced a write request."
>
> If that information is not necessarily meaningful, I'm not sure that's a
> problem except in configuration.
>
>
> ...Now, if you wanted to talk about bitmaps that associate with a
> Backend instead of a Node...
But it's not about bitmaps on intermediate nodes, quite the opposite.
It's about bitmaps on roots but write requests happening on intermediate
nodes.
Say you have a node I and two filter nodes A and B using it (and they
are OK with shared writers). There is a dirty bitmap on A.
Now when a write request goes through B, I will obviously have changed,
and because A and B are filters, so will A. But the dirty bitmap on A
will still be clean.
My example was that when you run a mirror over A, you won't see dirtying
from B. So you can't e.g. add a throttle driver between a mirror job
and the node you want to mirror, because the dirty bitmap on the
throttle driver will not be affected by accesses to the actual node.
Max
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- Re: [Qemu-block] [PATCH] blockdev-backup: enable non-root nodes for backup, Max Reitz, 2017/12/01
- Re: [Qemu-block] [PATCH] blockdev-backup: enable non-root nodes for backup, John Snow, 2017/12/04
- Re: [Qemu-block] [PATCH] blockdev-backup: enable non-root nodes for backup,
Max Reitz <=
- Re: [Qemu-block] [PATCH] blockdev-backup: enable non-root nodes for backup, John Snow, 2017/12/04
- Re: [Qemu-block] [PATCH] blockdev-backup: enable non-root nodes for backup, Max Reitz, 2017/12/08
- Re: [Qemu-block] [Qemu-devel] [PATCH] blockdev-backup: enable non-root nodes for backup, John Snow, 2017/12/08
- Re: [Qemu-block] [Qemu-devel] [PATCH] blockdev-backup: enable non-root nodes for backup, Max Reitz, 2017/12/11
- Re: [Qemu-block] [Qemu-devel] [PATCH] blockdev-backup: enable non-root nodes for backup, John Snow, 2017/12/11
- Re: [Qemu-block] [Qemu-devel] [PATCH] blockdev-backup: enable non-root nodes for backup, Max Reitz, 2017/12/11
- Re: [Qemu-block] [Qemu-devel] [PATCH] blockdev-backup: enable non-root nodes for backup, John Snow, 2017/12/11