On Mon, Jul 15, 2013 at 6:04 PM, Matthew Miller
<mattdm(a)fedoraproject.org> wrote:
On Mon, Jul 15, 2013 at 01:21:27PM +0100, Richard W.M. Jones wrote:
> > Is the compressed image still seekable? If yes, that constrains the
> > window/block size and limits the gains from switching compressors.
> Dan's answer covered one aspect of this: are qcow2 compressed
> images seekable, answer: yes, of course!
> But there's another answer for xz images. Are these seekable?
> Yes. Surprisingly. I've written the code for it:
>
https://rwmj.wordpress.com/2013/06/24/xz-plugin-for-nbdkit/#content
> *However* you have to prepare the xz images correctly for this to
> happen (using the --block-size argument, see blog posting above).
> Images created using standard xz parameters won't be seekable. I
> suggest it's a good idea that we do that for the cloud images, since
> the penalty is only about 1% and it makes them a lot more useful if
> you can use them without uncompressing them.
Interesting. This would probably be a RFE against appliance-tools (and in
the future ImageFactory), for producing raw.xz images in that way.
Or, bigger picture, maybe a future qcow2 format could support this natively?
Confused. Support what? Your comment above indicates that compressed
qcow2 images are seekable already.
...Juerg
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Matthew Miller ☁☁☁ Fedora Cloud Architect ☁☁☁ <mattdm(a)fedoraproject.org>
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