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>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.

From: Aryeh Friedman [mailto:aryeh.friedman at gmail.com]
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 <philip.day at hp.com<mailto:philip.day at hp.com>> 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
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