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Re: [Qemu-devel] [RFC 0/8] block: Live backup prototype
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [RFC 0/8] block: Live backup prototype |
Date: |
Mon, 11 Mar 2013 15:27:34 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Mon, Mar 11, 2013 at 09:26:26AM +0000, Dietmar Maurer wrote:
> > > > We track zero blocks at 4KB level to get small backup files. Restore
> > > > can handle those blocks differently, either pre-allocate or create
> > > > holes. That
> > > can even be a restore option.
> > >
> > > You are right, the behavior can be set at restore time.
> > >
> > > I'm curious how much of a win the 4 KB zero detection is on random
> > > Linux or Windows guest images. Have you collected numbers?
> >
> > Well, seems that it does not help much - it saves about 0.2% space. So maybe
> > we can remove that feature (and increase address space in the VMA format
> > instead).
>
> Sorry, I need to correct myself - I had a bug in the code.
>
> I can see space reduction up to 4% using this feature. Considering the fact
> that it
> comes at no cost, it would be stupid to remove it.
Okay, looks like it's useful but not a huge win.
In the NBD approach pipelining writes (or discards) ought to make 4 KB
zero blocks usable without overhead.
Stefan
- Re: [Qemu-devel] [RFC 3/8] backup: write to BlockDriverState instead of BackupDumpFunc, (continued)
- Re: [Qemu-devel] [RFC 0/8] block: Live backup prototype, Dietmar Maurer, 2013/03/10
- Re: [Qemu-devel] [RFC 0/8] block: Live backup prototype, Stefan Hajnoczi, 2013/03/10
- Re: [Qemu-devel] [RFC 0/8] block: Live backup prototype, Dietmar Maurer, 2013/03/10
- Re: [Qemu-devel] [RFC 0/8] block: Live backup prototype, Stefan Hajnoczi, 2013/03/10
- Re: [Qemu-devel] [RFC 0/8] block: Live backup prototype, Dietmar Maurer, 2013/03/11
- Re: [Qemu-devel] [RFC 0/8] block: Live backup prototype, Dietmar Maurer, 2013/03/11
- Re: [Qemu-devel] [RFC 0/8] block: Live backup prototype,
Stefan Hajnoczi <=
- Re: [Qemu-devel] [RFC 0/8] block: Live backup prototype, Dietmar Maurer, 2013/03/11
- Re: [Qemu-devel] [RFC 0/8] block: Live backup prototype, Stefan Hajnoczi, 2013/03/11
Re: [Qemu-devel] [RFC 0/8] block: Live backup prototype, Dietmar Maurer, 2013/03/10