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Date: Fri, 11 Nov 2011 16:43:18 -0600
From: Ryan Harper <ryanh@us.ibm.com>
Message-ID: <20111111224318.GC6036@us.ibm.com>
References: <4EBC683C.7090700@codemonkey.ws>
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In-Reply-To: <4EBC683C.7090700@codemonkey.ws>
Subject: Re: [Qemu-devel] Storage requirements for live migration
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To: Anthony Liguori <anthony@codemonkey.ws>
Cc: Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>, Juan Quintela <quintela@redhat.com>, qemu-devel <qemu-devel@nongnu.org>, Avi Kivity <avi@redhat.com>, Christoph Hellwig <hch@lst.de>

> == Image Formats ==
> 
> Image formats are not safe to use with live migration.  The reason is that 
> QEMU caches data for image formats and does not have a mechanism to flush 
> those caches.  The following attempts to describe the issues with the 
> various formats
> 
> === QCOW2 ===
> 
> QCOW2 caches two forms of data, cluster metadata (L1/L2 data, refcount 
> table, etc) and mutable header information (file size, snapshot entries, 
> etc).
> 
> This data needs to be discarded before after migration starts.

before after?

pick one =)


-- 
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
ryanh@us.ibm.com