[openstack-dev] [nova] usefulness of device parameter at volumeAttachment

Daniel P. Berrange berrange at redhat.com
Tue May 26 10:13:26 UTC 2015


On Sat, May 23, 2015 at 11:00:32AM +0200, Géza Gémes wrote:
> Hi,
> 
> When someone calls nova volume-attach or the block-device-mapping parameter
> at boot, it is possible to specify a device name for the guest. However I
> couldn't find any guest OS which would honor this. E.g. with libvirt/kvm, if
> the guest has two virtio disks already (vda and vdb), specifying vdf would
> be ignored and the disk will be attached as vdc in the guest.
> I propose to deprecate this option and at boot where it is not optional to
> accept only auto as an option.

This was a design mistake in the original API which we can't now remove
without breaking backcompatibility. While it is still supported, many
hypervisors will completely ignore it, so we discourage people from ever
using it. Just allow the hypervisor and/or guest OS to pick the device
name

Regards,
Daniel
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