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From Yoshikazu Nojima <m...@ynojima.net>
Subject Re: [RFC] adding volume provisioning method option
Date Sat, 01 Feb 2014 06:38:32 GMT
>I don't think preallocation=metadata is required for sparse qcow2.
>Just if you want it to NOT be sparse for metadata.

I think it is required. Please see the output below. Only
"metadata.img" is a sparse file.

==============
[root@ut1-qmb-rd5c test]# qemu-img create -f qcow2 -o
preallocation=off off.img 3G
Formatting 'off.img', fmt=qcow2 size=3221225472 encryption=off
cluster_size=65536 preallocation='off'
[root@ut1-qmb-rd5c test]# qemu-img create -f qcow2 -o
preallocation=metadata metadata.img 3G
Formatting 'metadata.img', fmt=qcow2 size=3221225472 encryption=off
cluster_size=65536 preallocation='metadata'
[root@ut1-qmb-rd5c test]# qemu-img create -f qcow2 -o
preallocation=full full.img 3G
Formatting 'full.img', fmt=qcow2 size=3221225472 encryption=off
cluster_size=65536 preallocation='full'
[root@ut1-qmb-rd5c test]# qemu-img create -f qcow2 no_option.img 3G
Formatting 'no_option.img', fmt=qcow2 size=3221225472 encryption=off
cluster_size=65536
[root@ut1-qmb-rd5c test]# ls -alhs
total 3.1G
4.0K drwxr-xr-x  2 root root 4.0K Feb  1 06:29 .
4.0K dr-xr-x---. 5 root root 4.0K Feb  1 06:19 ..
3.1G -rw-r--r--  1 root root 3.1G Feb  1 06:23 full.img
592K -rw-r--r--  1 root root 3.1G Feb  1 06:21 metadata.img
136K -rw-r--r--  1 root root 256K Feb  1 06:29 no_option.img
136K -rw-r--r--  1 root root 256K Feb  1 06:21 off.img
==============


>I also remember hearing that either recent qemu-img has a decent
>preallocation by default now, or that performance has improved such
>that it doesn't matter. Will need to do some reading to remember, but
>I think I remember hearing it's not a big deal nowadays.

Ummm. I tested with "qemu-img version 0.12.1," and I confirmed the
performance of "preallocation=off" is worse than
"preallocation=metadata",
but it may be not true with latest qemu. I will test it.

Thank you for your comment!

Regards,


2014-01-31 Marcus <shadowsor@gmail.com>:
> I don't think preallocation=metadata is required for sparse qcow2.
> Just if you want it to NOT be sparse for metadata.
>
> I also remember hearing that either recent qemu-img has a decent
> preallocation by default now, or that performance has improved such
> that it doesn't matter. Will need to do some reading to remember, but
> I think I remember hearing it's not a big deal nowadays.
>
> On Fri, Jan 31, 2014 at 10:04 PM, Yoshikazu Nojima <mail@ynojima.net> wrote:
>> Hello Nux,
>>
>> Thank you for your comment. I will prepare feature specification.
>>
>> Regards,
>>
>> 2014-01-31 Nux! <nux@li.nux.ro>:
>>> On 31.01.2014 20:24, Yoshikazu Nojima wrote:
>>>>
>>>> Afternoon All,
>>>>
>>>> Is there anyone working on adding volume provisioning method option?
>>>> As you know, thin provisioning of a volume save consumption of a
>>>> storage, and fat provisioning improves IOPS performance.
>>>> Especially, Qcow2 can save storage consumption and achive relatively
>>>> better performance than default by provisioning a volume with an
>>>> option "preallocation=metadata", which makes an image file a sparse
>>>> file.
>>>>
>>>> http://itscblog.tamu.edu/improve-disk-io-performance-in-kvm/#.232---preallocation
>>>>
>>>> Any thoughts about this?
>>>> If it is ok, I will write a feature specification on confluence and
>>>> start implementation.
>>>>
>>>> Regards,
>>>> Noji
>>>>
>>>>
>>>> Yoshikazu Nojima <mail@ynojima.net>
>>>
>>>
>>> Hello,
>>>
>>> I thought preallocation=metadata is common practice since years. Now I find
>>> out ACS doesn't actually use it?
>>> If so, this is really _bad_ and needs to be fixed ASAP...
>>>
>>> Thanks Noji
>>>
>>> --
>>> Sent from the Delta quadrant using Borg technology!
>>>
>>> Nux!
>>> www.nux.ro

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