openstack team mailing list archive

[Scott Moser <smoser@xxxxxxxxxx>]

On Wed, 6 Mar 2013, Pádraig Brady wrote:

> On 03/05/2013 02:04 PM, Scott Moser wrote:
> > On Tue, 5 Mar 2013, Sylvain Bauza wrote:
> >
> >> If you look at
> >> http://www.pixelbeat.org/docs/openstack_libvirt_images/#1361764412, you'll see
> >> that resize2fs is performed. But there is a caveat with RHEL6 which is Linux
> >> 2.6 (contrary to Ubuntu 12.04 which is Linux 3.0).
> >> If you look at "man resize2fs" :
> >
> > Please don't do this, or rely on this.  Having the hypervisor do this for
> > your guest is simply wrong.  Hypervisors should know little to nothing
> > about the internals of the instances they're launching.
>
> Just to point out the alternative for when the VM doesn't
> have the smarts to resize itself, is to use something like virt-resize:
> https://blueprints.launchpad.net/nova/+spec/resize-no-raw


Using libguestfs is worlds better than having the host "directly" do it.
But really whats happening here is *still* something with very little
information mucking with (and possibly breaking) the inside of a disk
image.  The more we consider that a "bucket of bytes" the better.

If you are using libguestfs, chances are you're using it from your distro,
and patching it to deal with a new filesystem (or otherwise get the update
to your hostOS) is still problematic.

Just let/expect the guest do it, and we'll avoid a whole silly game of cat
and mouse that doesn't even have to be played.

When was the last time you updated your bios on your laptop so you could
use a new linux filesystem?  That sounds silly, doesn't it.  Having
openstack reach inside the contents of the disk is just as silly.

One of the major benefits of having cloud-init direct the partition resize
*and* subsequent filesystem resize is that the user can (in user-data)
disable this!  (currently the initramfs doesn't take any instruction from
user-data, so disabling it isn't really a possibility).  perhaps they
didn't want that extra instance-store space to be part of the root
filesystem.

If you put that function inside the hypervisor, you either can't do it, of
you have to expose some silly api-launch parameter of
"do_not_modify_disk".  It complicates the API and complicates the host.