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

From: Avi Kivity
Subject: Re: [Qemu-devel] [PATCH 0/7] qed: Add QEMU Enhanced Disk format
Date: Mon, 27 Sep 2010 12:13:02 +0200
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20100921 Fedora/3.1.4-1.fc13 Lightning/1.0b3pre Thunderbird/3.1.4

 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

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.

error compiling committee.c: too many arguments to function

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