Hi Oliver,
We have several CephFS on EC pool deployments, one been in production for a while, the others about to pending all the Bluestore+EC fixes in 12.2.7 😊 Firstly as John and Greg have said, you don't need SSD cache pool at all. Secondly, regarding k/m, it depends on how many hosts or racks you have, and how many failures you want to tolerate. For our smallest pool with only 8 hosts in 4 different racks and 2 different pairs of switches (note: we consider switch failure more common than rack cooling or power failure), we're using 4/2 with failure domain = host. We currently use this for SSD scratch storage for HPC. For one of our larger pools, with 24 hosts over 6 different racks and 6 different pairs of switches, we're using 4:2 with failure domain = rack. For another pool with similar host count but not spread over so many pairs of switches, we're using 6:3 and failure domain = host. Also keep in mind that a higher value of k/m may give you more throughput but increase latency especially for small files, so it also depends on how important performance is and what kind of file size you store on your CephFS. Cheers, Linh ________________________________ From: ceph-users <ceph-users-boun...@lists.ceph.com> on behalf of Oliver Schulz <oliver.sch...@tu-dortmund.de> Sent: Sunday, 15 July 2018 9:46:16 PM To: ceph-users Subject: [ceph-users] CephFS with erasure coding, do I need a cache-pool? 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)? * 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? * Will it be sufficient to have k+m racks, resp. failure domains? 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<http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com>
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