Hi Kenneth, I did a migration from 2 to 3 pool layout recently. The only way to do this within ceph at the moment seems to be to create a second ceph fs with the new layout, rsync everything over and delete the old ceph fs. I had enough spare capacity and room for the extra PGs to do that. This requires downtime during the final rsync. Having done the migration, I don't really see any difference in performance or FS stability. It looks like the extra replicated default data pool does not have such a large impact and probably only in rare situations. I usually see no activity on it. Since the 2-pool layout will not run out of support, maybe it is not really that important to migrate? I didn't hear anything about in which situation it may make a decisive difference, the recommendation is formulated rather weakly. Maybe there are some future changes where this becomes important, but this would need to be answered by a developer. If you can't afford the downtime and are happy with how it works, I wouldn't bother too much. Would be nice to hear a bit more from someone with technical insight on code level. Best regards, ================= Frank Schilder AIT Risø Campus Bygning 109, rum S14 ________________________________________ From: Kenneth Waegeman <kenneth.waegeman(a)ugent.be> Sent: 07 May 2020 10:48:14 To: ceph-users(a)ceph.io Subject: [ceph-users] Re: cephfs change/migrate default data pool Someone an idea /experience if this is possible ? :) On 29/04/2020 14:56, Kenneth Waegeman wrote: _______________________________________________ ceph-users mailing list -- ceph-users(a)ceph.io To unsubscribe send an email to ceph-users-leave(a)ceph.io

Hi Frank, Patrick, I tried to create a cephfs elsewhere and got the warning, that's what got my attention. Nothing is broken, but I thought it could have impact on performance. Very good to know it's not that bad! Thanks!! Kenneth On 07/05/2020 23:31, Patrick Donnelly wrote: > On Wed, Apr 29, 2020 at 5:56 AM Kenneth Waegeman > <kenneth.waegeman(a)ugent.be> wrote: >> I read in some release notes it is recommended to have your default data >> pool replicated and use erasure coded pools as additional pools through >> layouts. We have still a cephfs with +-1PB usage with a EC default pool. >> Is there a way to change the default pool or some other kind of >> migration without having to recreate the FS? > Not until something like [1] is implemented. > > If it's not broken for you, don't fix it. > > [1] https://tracker.ceph.com/issues/40285 >