On 7 déc. 2009, at 10:57, Richard W.M. Jones wrote:
On Tue, Dec 01, 2009 at 04:08:38PM +0100, Pierre Riteau wrote:
For a project of mine I would like to create VMs from tarballs of root filesystems. I would like to use libguestfs since this is exactly what the tar2vm.sh guestfish recipe does.
However, I need to extract tarballs that are in the hundreds of megabytes, but my tests showed that performance is very low, both with tgz-in and with guestmount (sorry I don't have the numbers any more, but it was something like more than one hour to extract a tarball containing a Debian Lenny installation).
Is there any way to drastically improve libguestfs' performance?
First of all, read:
http://libguestfs.org/FAQ.html#slow
Using tar-in/tgz-in to copy the tarball into the appliance is always going to be slow. I would think you should get better performance if you write the tarball into an ISO first, and attach that. Something like:
mkisofs -JR -o cd.iso the_tarball.tar.gz
guestfish -a guest.img -a cd.iso [...]
<fs> mkmountpoint /guest <fs> mkmountpoint /cd [...] <fs> mount /dev/sdb /cd [...] <fs> debug sh "tar xcf /cd/the_tarball.tar.gz /guest"
I got it to work using the following sequence: $ guestfish -a guest.img -a cd.iso run sfdiskM /dev/sda "," mkfs ext3 /dev/sda1 mkmountpoint /guest mkmountpoint /cd mount /dev/sda1 /guest mount /dev/sdb /cd debug sh "tar -C /sysroot/guest -xzf /sysroot/cd/the_tarball.tar.gz" This is much better (on my test system it writes at about 15 MB/s). However, it is still far from what the hardware can do (more than 60 MB/s). Now the last problem is that I need to install a bootloader. Can I easily install grub in the appliance, or do I need to recreate a new one?
However we found experimentally that the fastest method of all for creating distributions was to prebuild an ext2/3/4 image, and 'dd' it over to the target partition, then resize it to the final (larger) size. This method is extremely quick, enabling us to build Fedora images in just a minute or two:
http://rwmj.wordpress.com/2009/11/23/prebuilt-distributions-part-2/#content
I've read your blog, this is interesting. I will see how I can leverage that. -- Pierre Riteau -- http://perso.univ-rennes1.fr/pierre.riteau/