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[Qemu-devel] Re: [RFC][STABLE 0.13] Revert "qcow2: Use bdrv_(p)write_syn


From: Avi Kivity
Subject: [Qemu-devel] Re: [RFC][STABLE 0.13] Revert "qcow2: Use bdrv_(p)write_sync for metadata writes"
Date: Wed, 25 Aug 2010 17:03:08 +0300
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.8) Gecko/20100806 Fedora/3.1.2-1.fc13 Thunderbird/3.1.2

 On 08/25/2010 04:46 PM, Anthony Liguori wrote:
On 08/25/2010 08:23 AM, Avi Kivity wrote:
 On 08/25/2010 03:46 PM, Anthony Liguori wrote:

If we had another disk format that only supported growth and metadata for a backing file, can you think of another failure scenario?

btw, only supporting growth is a step backwards. Currently file-backed disks keep growing even the guest-used storage doesn't grow, since once we allocate something we never release it. But eventually guests will start using TRIM or DISCARD or however it's called, and then we can expose it and reclaim unused blocks.

BTW, something that had the features of qcow2 that people actually used andwas fully asynchronous, performed well, and had a high degree of confidence in data integrity would be a major step forward, not backwards.


TRIM/DISCARD is not a feature that people use (esp. as it's not available) but we do want to support it in our image formats.

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