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Re: [Qemu-devel] [PATCH V18 0/6] add-cow file format
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH V18 0/6] add-cow file format |
Date: |
Thu, 18 Apr 2013 12:06:10 +0200 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Wed, Apr 10, 2013 at 04:11:47PM +0800, Dong Xu Wang wrote:
> It will introduce a new file format: add-cow.
>
> The add-cow file format makes it possible to perform copy-on-write on top of
> a raw disk image. When we know that no backing file clusters remain visible
> (e.g. we have streamed the entire image and copied all data from the backing
> file), then it is possible to discard the add-cow file and use the raw image
> file directly.
>
> This feature adds the copy-on-write feature to raw files (which cannot support
> it natively) while allowing us to get full performance again later when we no
> longer need copy-on-write.
>
> add-cow can benefit from other available functions, such as path_has_protocol
> and qed_read_string, so we will make them public.
>
> snapshot_blkdev are not supported now for add-cow. Will add it in futher
> patches.
>
> These patches are using QemuOpts parser, former patches could be found here:
> http://patchwork.ozlabs.org/patch/235300/
>
>
> v17 -> v18:
> 1) remove version field.
> 2) header size is maximum value and cluster size value.
> 3) fix type.
> 4) move struct to source file.
> 5) cluster_size->table_size.
> 6) use error_report, not fprintf.
> 7) remove version field from header.
> 8) header_size is MAX(cluster_size, 4096).
> 9) introduce s->cluster_sectors.
> 10) use BLKDBG_L2_LOAD/UPDATE.
> 11) add 037 and 038 tests.
Left a few comments but the series is close.
The biggest practical issue is serialized allocating writes.
Installation or multi-threaded write workloads may be quite slow since
only one read request is processed at a time. This can be solved later.
Stefan
- [Qemu-devel] [PATCH V18 0/6] add-cow file format, Dong Xu Wang, 2013/04/10
- [Qemu-devel] [PATCH V18 1/6] docs: document for add-cow file format, Dong Xu Wang, 2013/04/10
- [Qemu-devel] [PATCH V18 2/6] make path_has_protocol non static, Dong Xu Wang, 2013/04/10
- [Qemu-devel] [PATCH V18 3/6] qed_read_string to bdrv_read_string, Dong Xu Wang, 2013/04/10
- [Qemu-devel] [PATCH V18 4/6] rename qcow2-cache.c to block-cache.c, Dong Xu Wang, 2013/04/10
- [Qemu-devel] [PATCH V18 5/6] add-cow file format core code., Dong Xu Wang, 2013/04/10
- [Qemu-devel] [PATCH V18 6/6] qemu-iotests: add add-cow iotests support, Dong Xu Wang, 2013/04/10
- Re: [Qemu-devel] [PATCH V18 0/6] add-cow file format,
Stefan Hajnoczi <=