Sage, I guess this will be a problem with the cache pool when you do the export for the first time. However, after the first export is done, the diff data will be read and copied across and looking at the cache pool, I would say the diff data will be there anyway as the changes are going to be considered as hot data by the pool as it has been recently changed. So, I do not expect the delta exports squeeze too much data from the cache pool. That is if I got the understanding of how cache pools work.
Andrei ----- Original Message ----- From: "Sage Weil" <sw...@redhat.com> To: "Andrei Mikhailovsky" <and...@arhont.com> Cc: "Robert LeBlanc" <rob...@leblancnet.us>, ceph-users@lists.ceph.com Sent: Friday, 22 August, 2014 10:34:24 PM Subject: Re: [ceph-users] pool with cache pool and rbd export On Fri, 22 Aug 2014, Andrei Mikhailovsky wrote: > So it looks like using rbd export / import will negatively effect the > client performance, which is unfortunate. Is this really the case? Any > plans on changing this behavior in future versions of ceph? There will always be some impact from import/export as you are incurring IO load on the system. But yes, in the cache case, this isn't very nice. In master we've added the ability to avoid promoting objects on individual reads unless we've seen some previous activity. This isn't backported to firefly yet (although that is likely). Even so, someone needs to do a bit of testing to verify that the rbd export pattern incurs only a single read on the objects and will avoid a promotion in the general case. sage > > Cheers > > Andrei > > > ----- Original Message ----- > From: "Robert LeBlanc" <rob...@leblancnet.us> > To: "Andrei Mikhailovsky" <and...@arhont.com> > Cc: ceph-users@lists.ceph.com > Sent: Friday, 22 August, 2014 8:21:08 PM > Subject: Re: [ceph-users] pool with cache pool and rbd export > > > My understanding is that all reads are copied to the cache pool. This would > indicate that cache will be evicted. I don't know to what extent this will > affect the hot cache because we have not used a cache pool yet. I'm currently > looking into bcache fronting the disks to provide caching there. > > > Robert LeBlanc > > > > On Fri, Aug 22, 2014 at 12:41 PM, Andrei Mikhailovsky < and...@arhont.com > > wrote: > > > Hello guys, > > I am planning to perform regular rbd pool off-site backup with rbd export and > export-diff. I've got a small ceph firefly cluster with an active writeback > cache pool made of couple of osds. I've got the following question which I > hope the ceph community could answer: > > Will this rbd export or import operations affect the active hot data in the > cache pool, thus evicting from the cache pool the real hot data used by the > clients. Or does the process of rbd export/import effect only the osds and > does not touch the cache pool? > > Many thanks > > Andrei > > _______________________________________________ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > _______________________________________________ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
