openstack team mailing list archive

[John Garbutt <John.Garbutt@xxxxxxxxxx>]

You can see what XenAPI exposes here:
 http://docs.vmd.citrix.com/XenServer/6.0.0/1.0/en_gb/api/?c=VBD

I think the only thing you can influence when plugging in the disk is the “userdevice” which is the disk position: 0,1,2…
When you have attached the disk you can find out the “device” name, such as /dev/xvda

I don't know about Xen with libvirt. But from the previous discussion it seems using the disk position would also work with KVM?

It seems disk position is also suitably OS agnostic, but I may have missed something there.

For backwards compatibility, we could make a "best effort" of translating the specified device name to a position. But as mentioned already, it seems fraught with danger in the general case.

I like the idea of an extra field to help report to the user what the likely device name is, if available. It would allow us to spot when the above "guessing" did not gone the way we had hoped.

Related to this, there is a limitation in Xen (a limitation in the blkbk/blkfrnt protocol I am told) that means you can't cancel the operation of removing a disk from a VM. So if the disk is in use, it may return with an exception saying the disk is in-use, but as soon as the disk can be released, it will be removed anyway. Currently, nova isn't very good at expressing to the user that this is what is happening:
https://bugs.launchpad.net/nova/+bug/1030108

Cheers,
John
 
> From: openstack-bounces+john.garbutt=citrix.com@xxxxxxxxxxxxxxxxxxx [mailto:openstack-bounces+john.garbutt=citrix.com@xxxxxxxxxxxxxxxxxxx] On Behalf Of Wangpan
> Sent: 15 August 2012 5:11
> To: Vishvananda Ishaya
> Cc: openstack
> Subject: Re: [Openstack] [nova] Disk attachment consistency
> > This is definitely another solution, although it seems less usable than the device serial number which can be an arbitrary string. If this works for xen though, that would be a plus.
> > Vish
> I don't have a Xen hypervisor in hand, so anybody else can try it on Xen ? thanks