On 06/13/2014 08:03 AM, Day, Phil wrote:
>Theoretically impossible to reduce disk unless you have some really
nasty guest additions.
That's what I thought -- but many of the drivers seem to at least
partially support it based on the code, hence the question on here to
find out of that is really supported and works -- or is just
inconsistent error checking across drivers.
My grumpy dev answer is that what works is not resizing down. I'm
familiar with the xen driver resize operation and will say that it does
work when the guest filesystem and partition sizes are accommodating,
but there's no good way to know whether or not it will succeed without
actually trying it. So when it fails it's after someone was waiting on
a resize that seemed like it was working and then suddenly didn't.
If we want to aim for what's going to work consistently across drivers,
it's probably going to end up being not resizing disks down.
*From:*Aryeh Friedman [mailto:[email protected]]
*Sent:* 13 June 2014 11:12
*To:* OpenStack Development Mailing List (not for usage questions)
*Subject:* Re: [openstack-dev] [nova] Do any hyperviors allow disk
reduction as part of resize ?
Theoretically impossible to reduce disk unless you have some really
nasty guest additions.
On Fri, Jun 13, 2014 at 6:02 AM, Day, Phil <[email protected]
<mailto:[email protected]>> wrote:
Hi Folks,
I was looking at the resize code in libvirt, and it has checks
which raise an exception if the target root or ephemeral disks are
smaller than the current ones -- which seems fair enough I guess
(you can't drop arbitary disk content on resize), except that the
because the check is in the virt driver the effect is to just
ignore the request (the instance remains active rather than going
to resize-verify).
It made me wonder if there were any hypervisors that actually
allow this, and if not wouldn't it be better to move the check to
the API layer so that the request can be failed rather than
silently ignored ?
As far as I can see:
baremetal: Doesn't support resize
hyperv: Checks only for root disk
(https://github.com/openstack/nova/blob/master/nova/virt/hyperv/migrationops.py#L99-L108
)
libvirt: fails for a reduction of either root or ephemeral
(https://github.com/openstack/nova/blob/master/nova/virt/libvirt/driver.py#L4918-L4923
)
vmware: doesn't seem to check at all ?
xen: Allows resize down for root but not for ephemeral
(https://github.com/openstack/nova/blob/master/nova/virt/xenapi/vmops.py#L1015-L1032
)
It feels kind of clumsy to have such a wide variation of behavior
across the drivers, and to have the check performed only in the
driver ?
Phil
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--
Aryeh M. Friedman, Lead Developer, http://www.PetiteCloud.org
<http://www.PetiteCloud.org>
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