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[Matt Riedemann <mriedem@xxxxxxxxxx>]

This seems like something that would have to be expressed from the
cinder side based on the volume type.

Currently the libvirt driver gets the os-brick volume connector and
passes that use_multipath value in here:

https://github.com/openstack/nova/blob/14.0.1/nova/virt/libvirt/driver.py#L1033

That's the connector that nova passes to os-initialize_connection in
cinder which gives back the connection_info used when connecting the
volume to the host.

So nova would need to know if it should use multipath or not before
that, which we could maybe get from the volume/volume_type if cinder
provided that information. Otherwise this is just how it's always
worked.

If cinder started providing that info, it would have to probably be in a
microversion in the cinder v3 API.

** Changed in: nova
   Importance: Undecided => Wishlist

** Changed in: nova
       Status: New => Opinion

** Summary changed:

- Use of iscsi_multipath should not be mandatory
+ Use of CONF.libvirt.volume_use_multipath should not be mandatory

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https://bugs.launchpad.net/bugs/1639350

Title:
  Use of CONF.libvirt.volume_use_multipath should not be mandatory

Status in OpenStack Compute (nova):
  Opinion
Status in os-brick:
  New

Bug description:
  Currently if iscsi_multipath is set in nova.conf we require ALL
  attachments to use multipath.  The problem with this is that it's not
  uncommon to have a mix of Cinder backends; one that supports multipath
  and one that doesn't.  The result with how we do this now is that you
  can have only one or the other but not both.

  We should be able to revert to single-path when multipath doesn't work
  for the volume; also might be worth considering if the multipath
  support should just be embedded as part of the volume object and skip
  the need to configure it in Nova at all.

  To reproduce, set up a default devstack with LIO and LVM; set
  nova.conf iscsi_multipath=True, restart nova.

  Create a volume, create an instance, try and attach the volume to the
  instance.

  Example stack trace here:
  http://paste.openstack.org/show/587939/

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