On Thu, Nov 11, 2021 at 7:55 AM Zakhar Kirpichenko <zakhar@xxxxxxxxx> wrote: > > Hi, > > I'm still trying to combat really bad read performance from HDD-backed > replicated pools, which is under 100 MB/s most of the time with 1 thread > and QD=1. I don't quite understand why the reads are that slow, i.e. much > slower than a single HDD, but do understand that Ceph clients read a PG > from primary OSD only. > > Since reads are immutable, is it possible to make Ceph clients read PG in a > RAID1-like fashion, i.e. if a PG has a primary OSD and two replicas, is it > possible to read all 3 OSDs in parallel for a 3x performance gain? It sounds like a compelling idea but you have to consider read-write ordering: you have the potential for a read on a replica returning out-of-date data. There are strategies to resolve that but you have to ask yourself why? RADOS specifically scales by adding more objects/PGs. This should naturally spread load on primary OSDs across the cluster. Replicas are for redundancy not for improving (read) throughput. -- Patrick Donnelly, Ph.D. He / Him / His Principal Software Engineer Red Hat, Inc. GPG: 19F28A586F808C2402351B93C3301A3E258DD79D _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
 |