On Tue, Nov 20, 2018 at 9:50 PM Vlad Kopylov <vladk...@gmail.com> wrote:
> I see the point, but not for the read case: > no overhead for just choosing or let Mount option choose read replica. > > This is simple feature that can be implemented, that will save many > people bandwidth in really distributed cases. > This is actually much more complicated than it sounds. Allowing reads from the replica OSDs while still routing writes through a different primary OSD introduces a great many consistency issues. We've tried adding very limited support for this read-from-replica scenario in special cases, but have had to roll them all back due to edge cases where they don't work. I understand why you want it, but it's definitely not a simple feature. :( -Greg > > Main issue this surfaces is that RADOS maps ignore clients - they just > see cluster. There should be the part of RADOS map unique or possibly > unique for each client connection. > > Lets file feature request? > > p.s. honestly, I don't see why anyone would use ceph for local network > RAID setups, there are other simple solutions out there even in your > own RedHat shop. > On Tue, Nov 20, 2018 at 8:38 PM Patrick Donnelly <pdonn...@redhat.com> > wrote: > > > > You either need to accept that reads/writes will land on different data > centers, primary OSD for a given pool is always in the desired data center, > or some other non-Ceph solution which will have either expensive, eventual, > or false consistency. > > > > On Fri, Nov 16, 2018, 10:07 AM Vlad Kopylov <vladk...@gmail.com wrote: > >> > >> This is what Jean suggested. I understand it and it works with primary. > >> But what I need is for all clients to access same files, not separate > sets (like red blue green) > >> > >> Thanks Konstantin. > >> > >> On Fri, Nov 16, 2018 at 3:43 AM Konstantin Shalygin <k0...@k0ste.ru> > wrote: > >>> > >>> On 11/16/18 11:57 AM, Vlad Kopylov wrote: > >>> > Exactly. But write operations should go to all nodes. > >>> > >>> This can be set via primary affinity [1], when a ceph client reads or > >>> writes data, it always contacts the primary OSD in the acting set. > >>> > >>> > >>> If u want to totally segregate IO, you can use device classes: > >>> > >>> Just create osds with different classes: > >>> > >>> dc1 > >>> > >>> host1 > >>> > >>> red osd.0 primary > >>> > >>> blue osd.1 > >>> > >>> green osd.2 > >>> > >>> dc2 > >>> > >>> host2 > >>> > >>> red osd.3 > >>> > >>> blue osd.4 primary > >>> > >>> green osd.5 > >>> > >>> dc3 > >>> > >>> host3 > >>> > >>> red osd.6 > >>> > >>> blue osd.7 > >>> > >>> green osd.8 primary > >>> > >>> > >>> create 3 crush rules: > >>> > >>> ceph osd crush rule create-replicated red default host red > >>> > >>> ceph osd crush rule create-replicated blue default host blue > >>> > >>> ceph osd crush rule create-replicated green default host green > >>> > >>> > >>> and 3 pools: > >>> > >>> ceph osd pool create red 64 64 replicated red > >>> > >>> ceph osd pool create blue 64 64 replicated blue > >>> > >>> ceph osd pool create blue 64 64 replicated green > >>> > >>> > >>> [1] > >>> > http://docs.ceph.com/docs/master/rados/operations/crush-map/#primary-affinity > ' > >>> > >>> > >>> > >>> k > >>> > >> _______________________________________________ > >> 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 >
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