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Re: [Qemu-discuss] [Qemu-devel] Incremental drive-backup with dirty bitm

From: Kashyap Chamarthy
Subject: Re: [Qemu-discuss] [Qemu-devel] Incremental drive-backup with dirty bitmaps
Date: Thu, 24 Jan 2019 10:16:49 +0100
User-agent: Mutt/1.10.1 (2018-07-13)

On Wed, Jan 23, 2019 at 01:09:41PM -0600, Eric Blake wrote:
> On 1/23/19 12:08 PM, Bharadwaj Rayala wrote:

[...] # [Snip Eric's excellent exposition.]

> > What do you mean by issues? Do you mean any data/corruption bugs or lack of
> > some nice functionality that we are talking here?
> Lack of functionality.  In particular, the 4.0 commands
> block-dirty-bitmap-{enable,merge,disable} (or their 3.1 counterparts
> x-block-dirty-bitmap-*) are essential to the workflow of differential
> backups (without being able to manage bitmaps yourself, you can only get
> the weaker incremental backup, and that means qemu itself is clearing
> the bitmap out of under your feet on success, and where you are having
> to worry about completion-mode=grouped).
> > 
> > Thanks a lot Eric for spending your time in answering my queries. I dont
> > know if you work with Kashyap Chamarthy, but your help and his blogs are
> > lifesavers.
> Yes, Kashyap is trying to build solutions on top of the building blocks
> that I am working on, so we have collaborated several times on these
> types of issues (he does a lot better at blog posts extracted from my
> mailing list brain dumps).

I haven't kept up with incremental backups lately, as I've been swamped
with other work.  But two other documents that I can point to are these
[1][2] in the QEMU tree.  And their HTML-rendered versions are
here[3][4].  They're generated for 3.0.0; but these docs haven't changed
much since then.

Along with Eric's last year talk, also check out presentations from
previous KVM Forums from other Block Layer maintainers.

[2] https://git.qemu.org/?p=qemu.git;a=blob;f=docs/interop/bitmaps.rst


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