Re: [Qemu-devel] [PATCH 0/7] qed: Add QEMU Enhanced Disk format

[Avi Kivity <avi@redhat.com>]

  On 09/23/2010 05:41 PM, Stefan Hajnoczi wrote:
> QEMU Enhanced Disk format is a disk image format that forgoes features
> found in qcow2 in favor of better levels of performance and data
> integrity.  Due to its simpler on-disk layout, it is possible to safely
> perform metadata updates more efficiently.
>
> Installations, suspend-to-disk, and other allocation-heavy I/O workloads
> will see increased performance due to fewer I/Os and syncs.  Workloads
> that do not cause new clusters to be allocated will perform similar to
> raw images due to in-memory metadata caching.
>
> The format supports sparse disk images.  It does not rely on the host
> filesystem holes feature, making it a good choice for sparse disk images
> that need to be transferred over channels where holes are not supported.
>
> Backing files are supported so only deltas against a base image can be
> stored.
>
> The file format is extensible so that additional features can be added
> later with graceful compatibility handling.
>
> Internal snapshots are not supported.  This eliminates the need for
> additional metadata to track copy-on-write clusters.
>
> Compression and encryption are not supported.  They add complexity and can be
> implemented at other layers in the stack (i.e. inside the guest or on the
> host).  Encryption has been identified as a potential future extension and the
> file format allows for this.
>

IMO the file format should be part of this patchset.  Wikis are nice but 
they aren't a good place for authoritative documentation.

-- 
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