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[Qemu-devel] [Bug 1458239] Re: Use qed instead of qcow2 for "-snapshot"

From: Kevin Wolf
Subject: [Qemu-devel] [Bug 1458239] Re: Use qed instead of qcow2 for "-snapshot" functionality
Date: Wed, 27 May 2015 12:04:32 -0000

Unless you're using cache=writethrough (which is not the case with
-snapshot), qed has never been faster than qcow2 in a release. qed was
introduced in the same release as qcow2 introduced a writeback metadata
cache which improved performance with cache=none/writeback a lot (qemu
0.14). cache=writethrough gained the same optimisation as qed had with
qcow2's lazy_refcounts, which can optionally be enabled since qemu 1.2.

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  Use qed instead of qcow2 for "-snapshot" functionality

Status in QEMU:

Bug description:
  AFAIK, qed is better in performance  than qcow2, so why we still use
  qcow2 for internal snapshots ? patch is trivial.

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