[Qemu-devel] [Bug 1458239] [NEW] Use qed instead of qcow2 for "-snapshot" functionality

[Qemu-devel] [Bug 1458239] [NEW] Use qed instead of qcow2 for "-snapshot" functionality

[Коренберг Марк]

Public bug reported:

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

** Affects: qemu
     Importance: Undecided
         Status: New

** Summary changed:

- Used qed instead of qcow2 for "-snapshot" functionality
+ Use qed instead of qcow2 for "-snapshot" functionality

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Title:
  Use qed instead of qcow2 for "-snapshot" functionality

Status in QEMU:
  New

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

[Michael Tokarev]

I'm not sure I follow, why qed is better?  qed was an example/testing
format in an attempt to make qcow2 faster.  It succeeded in its task,
and qcow2 has been improved a lot after playing with qed. What's wrong
with qcow2 and why it is faster? How about providing some benchmarks?

** Changed in: qemu
       Status: New => Invalid

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Title:
  Use qed instead of qcow2 for "-snapshot" functionality

Status in QEMU:
  Invalid

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

[Коренберг Марк]

Sorry, I did not know tha qed is just experimental format. I thought
that qed is successor of qcow2. Can you add some links that qcow is not
worse than qed ? I did not make any benchmark, just read some articles

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Title:
  Use qed instead of qcow2 for "-snapshot" functionality

Status in QEMU:
  Invalid

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

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 534 bytes --]

On Sun, May 24, 2015 at 07:54:19AM -0000, Коренберг Марк wrote:
> Sorry, I did not know tha qed is just experimental format. I thought
> that qed is successor of qcow2. Can you add some links that qcow is not
> worse than qed ? I did not make any benchmark, just read some articles

Hi,
QED's write performance optimization has been added to qcow2 (-o
lazy_refcounts=on).

qcow2 has been optimized further in the meantime and is the recommended
image file format if raw lacks features that you need.

Stefan

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

[Paolo Bonzini]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256



On 26/05/2015 12:18, Stefan Hajnoczi wrote:
> On Sun, May 24, 2015 at 07:54:19AM -0000, Коренберг Марк wrote:
>> Sorry, I did not know tha qed is just experimental format. I
>> thought that qed is successor of qcow2. Can you add some links
>> that qcow is not worse than qed ? I did not make any benchmark,
>> just read some articles
> 
> Hi, QED's write performance optimization has been added to qcow2
> (-o lazy_refcounts=on).
> 
> qcow2 has been optimized further in the meantime and is the
> recommended image file format if raw lacks features that you need.

Also, -snapshots uses "cache=unsafe", so there should be no
performance difference between the two anyway.

Random idea: should qcow2 always use lazy refcounts if it receives
"cache=unsafe"?

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

[Коренберг Марк]

Ok, from which qemu versions, qcow2 is faster or equal to qed ?

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Title:
  Use qed instead of qcow2 for "-snapshot" functionality

Status in QEMU:
  Invalid

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

[Kevin Wolf]

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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Title:
  Use qed instead of qcow2 for "-snapshot" functionality

Status in QEMU:
  Invalid

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

[Коренберг Марк]

Huge thanks for detailed explanation.

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Title:
  Use qed instead of qcow2 for "-snapshot" functionality

Status in QEMU:
  Invalid

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

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1458239/+subscriptions