[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
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
libguestfs lets you edit virtual machines. Supports shell scripting,
bindings from many languages. http://et.redhat.com/~rjones/libguestfs/
See what it can do: http://et.redhat.com/~rjones/libguestfs/recipes.html