Comment 3 for bug 1314526

Reviewed: https://review.openstack.org/91722
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=bc45c56f102cdef58840e02b609a89f5278e8cce
Submitter: Jenkins
Branch: master

commit bc45c56f102cdef58840e02b609a89f5278e8cce
Author: Dmitry Borodaenko <email address hidden>
Date: Thu Nov 21 16:05:19 2013 -0800

    Improve shared storage checks for live migration

    Due to an assumption that libvirt live migrations work only when both
    instance path and disk data is shared between source and destination
    hosts (e.g. libvirt instances directory is on NFS), instance disks are
    removed from shared storage when instance path is not shared (e.g. Ceph
    RBD backend is enabled).

    Distinguish cases that require shared instance drive and shared libvirt
    instance directory. Reflect the fact that RBD backed instances have
    shared instance drive (and no shared libvirt instance directory) in the
    relevant conditionals.

    UpgradeImpact: Live migrations from or to a compute host running a
    version of Nova pre-dating this commit are disabled in order to
    eliminate possibility of data loss. Upgrade Nova on both the source and
    the target node before attempting a live migration.

    Closes-bug: 1250751
    Closes-bug: 1314526
    Co-authored-by: Ryan Moe <email address hidden>
    Co-authored-by: Yaguang Tang <email address hidden>
    Signed-off-by: Dmitry Borodaenko <email address hidden>
    Change-Id: I2755c59b4db736151000dae351fd776d3c15ca39