[libvirt] Changing the default for qcow2 creation

Philipp Hahn hahn at univention.de
Wed Nov 3 07:28:10 UTC 2010


Hello,

Am Dienstag 02 November 2010 23:45:59 schrieb Eric Blake:
> On 10/25/2010 08:06 AM, Richard W.M. Jones wrote:
> >> libvirt's qemu driver doesn't currently preallocate qcow2 metadata
> >> when creating a new image. Given the tiny disk space overhead of the
> >> metadata (0.02%) and the small processing overhead of pre-creation
> >> relative to subsequent creation on-the-fly, I suggest that the
> >> libvirt qemu driver is updated to pre-allocate metadata by default.
...
> Is this something that we should just globally enable if qemu supports
> it, or do we need some XML tunable to allow someone to skip the
> pre-allocation for some reason?

I don't know if its relevant, but if you create a qcow2 image, which is based 
on another base-image, you must not pass the option to pre-allocate, else you 
get the following error message:
  Backing file and preallocation cannot be used at the same time

Sincerely
Philipp Hahn
-- 
Philipp Hahn           Open Source Software Engineer      hahn at univention.de   
Univention GmbH        Linux for Your Business        fon: +49 421 22 232- 0
Mary-Somerville-Str.1  28359 Bremen                   fax: +49 421 22 232-99
                                                    http://www.univention.de
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