[Fedora-xen] Kickstart slowness with virt-install

[Hanks, Dan]

> -----Original Message-----
> From: Daniel P. Berrange [mailto:berrange at redhat.com]
> Sent: Wednesday, March 07, 2007 2:54 PM
> To: Hanks, Dan
> Cc: fedora-xen at redhat.com
> Subject: Re: [Fedora-xen] Kickstart slowness with virt-install
> 
> On Wed, Mar 07, 2007 at 01:50:43PM -0800, Hanks, Dan wrote:
> > Hi folks,
> >
> >
> >
> > I've been able to kickstart a number of VMs using the virt-install
tool,
> > and so far have had pretty good success. One aspect of these
installs
> > has me a bit concerned, though. In most cases, anytime the kickstart
> > needs to do intensive disk activity (such as formatting partitions,
or
> > installing all the rpms) there are noticible hangs, which I'm
guessing
> > come from some kind of IO wait. The result is that a kickstart which
> > should take < 10 minutes ends up taking a half-hour or so.
> 
> What kind of virtual disk image are you using for the guest ? A
partition
> or a file - if the latter is it sparse, or non-sparse. Basically
sparse
> files will be horribly slow because every time the host OS has to
extend
> the sparse file to allocate real blocks it needs to do a journal sync
on
> the host FS. This destroys performance of I/O from the guest until the
> sparse file is fully-allocated.

I'm using files. I've been using a command-line such as this for the
install:

virt-install -m "00:16:3e:00:00:01" -n hostname -r 500 --vcpus=2 -f
/var/lib/xen/images/myhost.xen.img -s 4 --nographics -p -l
ftp://host/fc6/distro/i386/os -x "ks=http://kshost/ks.cfg"

Adding --nonsparse into the args looks like it fixes the speed issues
(albeit adds a bit of extra time right up front to allocate the entire
disk image). I imagine using partitions instead of files would be faster
altogether. I'll have to explore that option (files are just so nice to
ship around when needed).

The verbiage for the virt-install command-line args is (to me) a bit
confusing in this matter:

"-- nonsparse       Don't use sparse files for disks. Note that this
will be significantly slower for guest creation"

What does the "slower" here refer to? Slower up-front time to create the
image file? Yes, but the actual install will be faster since it wont
have to keep allocating more space for the disk image. Thoughts? 

Thanks for your help--this was exactly the piece of information I
needed,

-- Dan