On Mon, Jul 16, 2018 at 1:25 AM John Spray <jsp...@redhat.com> wrote:
> On Sun, Jul 15, 2018 at 12:46 PM Oliver Schulz > <oliver.sch...@tu-dortmund.de> wrote: > > > > Dear all, > > > > we're planning a new Ceph-Clusterm, with CephFS as the > > main workload, and would like to use erasure coding to > > use the disks more efficiently. Access pattern will > > probably be more read- than write-heavy, on average. > > > > I don't have any practical experience with erasure- > > coded pools so far. > > > > I'd be glad for any hints / recommendations regarding > > these questions: > > > > * Is an SSD cache pool recommended/necessary for > > CephFS on an erasure-coded HDD pool (using Ceph > > Luminous and BlueStore)? > > Since Luminous, you can use an erasure coded pool (on bluestore) > directly as a CephFS data pool, no cache pool needed. > More than that, we'd really prefer you didn't use cache pools for anything. Just Say No. :) -Greg > > John > > > * What are good values for k/m for erasure coding in > > practice (assuming a cluster of about 300 OSDs), to > > make things robust and ease maintenance (ability to > > take a few nodes down)? Is k/m = 6/3 a good choice? > That will depend on your file sizes, IO patterns, and expected durability needs. I think 6+3 is a common one but I don't deal with many deployments. > > > > * Will it be sufficient to have k+m racks, resp. failure > > domains? > Generally, if you want CRUSH to select X "buckets" at any level, it's good to have at least X+1 choices for it to prevent mapping failures. But you could also do workaround like letting it choose (K+M)/2 racks and putting two shards in each rack. -Greg > > > > > > Cheers and thanks for any advice, > > > > Oliver > > _______________________________________________ > > 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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