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Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1)
From: |
Dietmar Maurer |
Subject: |
Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1) |
Date: |
Wed, 21 Nov 2012 13:25:20 +0000 |
> > AFAIK qcow2 file cannot store data out of order. In general, an backup
> > fd is not seekable, and we only want to do sequential writes. Image format
> always requires seekable fds?
>
> Ah, this is what you mean by "out of order". Just out of curiosity, what are
> these non-seekable backup fds usually?
/dev/nst0 ;-)
But there are better examples. Usually you want to use some kind of
compression, and you do that with existing tools:
# backup to stdout|gzip|...
A common usage scenario is to pipe a backup into a restore (copy)
# backup to stdout|ssh to remote host -c 'restore from stdin'
It is also a performance question. Seeks are terrible slow.
> In principle even for this qcow2 could be used as an image format, however
> the existing implementation wouldn't be of much use for you, so it loses
> quite a bit of its attractiveness.
>
> > Anyways, a qcow2 file is really complex beast - I am quite unsure if I
> > would use that for backup if it is possible.
> >
> > That would require any external tool to include >=50000 LOC
> >
> > The vma reader code is about 700 LOC (quite easy).
>
> So what? qemu-img is already there.
Anyways, you already pointed out that the existing implementation does not work.
But I already expected such discussion. So maybe it is better we simply pipe
all data to an external binary?
We just need to define a minimal protocol.
In future we can produce different archivers as independent/external binaries?
- Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1), (continued)
- Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1), Dietmar Maurer, 2012/11/23
- Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1), Dietmar Maurer, 2012/11/23
- Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1), Dietmar Maurer, 2012/11/23
- Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1), Paolo Bonzini, 2012/11/23
- Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1), Dietmar Maurer, 2012/11/23
- Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1), Kevin Wolf, 2012/11/23
- Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1), Markus Armbruster, 2012/11/23
- Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1),
Dietmar Maurer <=
- Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1), Kevin Wolf, 2012/11/21
- Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1), Dietmar Maurer, 2012/11/21
- Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1), Dietmar Maurer, 2012/11/23
- Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1), Kevin Wolf, 2012/11/23
- Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1), Dietmar Maurer, 2012/11/23
- Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1), Dietmar Maurer, 2012/11/23
- Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1), Kevin Wolf, 2012/11/23
- Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1), Dietmar Maurer, 2012/11/26
- Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1), Paolo Bonzini, 2012/11/26
- Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1), Dietmar Maurer, 2012/11/27