[Libguestfs] Re: libguestfs performance

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"

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