On Fri, Feb 16, 2018 at 5:36 AM, Jens-U. Mozdzen <jmozdzen@xxxxxx> wrote: > Dear list, hello Jason, > > you may have seen my message on the Ceph mailing list about RDB pool > migration - it's a common subject that pools were created in a sub-optimum > fashion and i. e. pgnum is (not yet) reducible, so we're looking into means > to "clone" an RBD pool into a new pool within the same cluster (including > snapshots). > > We had looked into creating a tool for this job, but soon noticed that we're > duplicating basic functionality of rbd-mirror. So we tested the following, > which worked out nicely: > > - create a test cluster (Ceph cluster plus an Openstack cluster using an RBD > pool) and some Openstack instances > > - create a second Ceph test cluster > > - stop Openstack > > - use rbd-mirror to clone the RBD pool from the first to the second Ceph > cluster (IOW aborting rbd-mirror once the initial coping was done) > > - recreate the RDB pool on the first cluster > > - use rbd-mirror to clone the mirrored pool back to the (newly created) pool > on the first cluster > > - start Openstack and work with the (recreated) pool on the first cluster > > So using rbd-mirror, we could clone an RBD pool's content to a differently > structured pool on the same cluster - by using an intermediate cluster. > > @Jason: Looking at the commit history for rbd-mirror, it seems you might be > able to shed some light on this: Do you see an easy way to modify rbd-mirror > in such a fashion that instead of mirroring to a pool on a different cluster > (having the same pool name as the original), mirroring would be to a pool on > the *same* cluster, (obviously having a pool different name)? > > From the "rbd cppool" perspective, a one-shot mode of operation would be > fully sufficient - but looking at the code, I have not even been able to > identify the spots where we might "cut away" the networking part, so that > rbd-mirror might do an intra-cluster job. > > Are you able to judge how much work would need to be done, in order to > create a one-shot, intra-cluster version of rbd-mirror? Might it even be > something that could be a simple enhancement? You might be interested in the deep-copy feature that will be included in the Mimic release. By running "rbd deep-copy <src-image> <dst-image>", it will fully copy the image, including snapshots and parentage, to a new image. There is also work-in-progress for online image migration [1] that will allow you to keep using the image while it's being migrated to a new destination image. Both of these are probably more suited to your needs than the heavy-weight RBD mirroring process -- especially if you are only interested in the first step since RBD mirroring now directly utilizes the deep-copy feature for the initial image sync. > Thank you for any information and / or opinion you care to share! > > With regards, > Jens > [1] https://github.com/ceph/ceph/pull/15831 -- Jason _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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