Sage, would it not be more effective to separate the data as internal and external in a sense. So all maintenance related activities will be classed as internal (like scrubbing, deep-scrubbing, import and export data, etc) and will not effect the cache and all other activities (really client io) will go through cache? Andrei ----- Original Message ----- From: "Sage Weil" <sweil@xxxxxxxxxx> To: "Andrei Mikhailovsky" <andrei at arhont.com> Cc: "Robert LeBlanc" <robert at leblancnet.us>, ceph-users at lists.ceph.com Sent: Friday, 22 August, 2014 10:34:24 PM Subject: Re: 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" <robert at leblancnet.us> > To: "Andrei Mikhailovsky" <andrei at arhont.com> > Cc: ceph-users at 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 < andrei at 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 at lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > _______________________________________________ > ceph-users mailing list > ceph-users at lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > >
 |