Comment 8 for bug 1209199

Reviewed: https://review.openstack.org/41469
Committed: http://github.com/openstack/cinder/commit/52291d6554f2275b228d7039d222bccfab164106
Submitter: Jenkins
Branch: master

commit 52291d6554f2275b228d7039d222bccfab164106
Author: Edward Hope-Morley <email address hidden>
Date: Mon Aug 12 17:46:38 2013 +0100

    Added copy-on-write support for all RBD cloning

    Up till now we only had copy-on-write for cloning from snapshot. This
    change optionally allows clone from volume to use copy-on-write
    instead of a doing a full copy each time. This should increase speed
    and reduce nearterm storage consumtion but could introduce some new
    risks e.g. excessively long clone chains and flatten storms. To avoid
    this, a new config option has been providedons are provided -
    rbd_max_clone_depth - which allows the user to limit the depth of a
    chain of clones i.e.

        a->b->c->d as opposed to a->b
                                  ->c
                                  ->d

    This will avoid flatten storms by breaking chains as they are formed
    and at an early, predefined stage.

    A second option - rbd_clone_from_volume_force_copy - allows the user
    to use a full copy as before i.e. disable COW for volume clones.

    Implements: blueprint use-copy-on-write-for-all-volume-cloning
    Fixes: bug #1209199

    Change-Id: Ia4a8a10c797cda2cf1ef3a2e9bd49f8c084ec977