Ceph RBD - High IOWait during the Writes

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Hi All,

We have recently deployed a new CEPH cluster Octopus 15.2.4 which consists
of

12 OSD Nodes(16 Core + 200GB RAM,  30x14TB disks, CentOS 8)
3 Mon Nodes (8 Cores + 15GB, CentOS 8)

We use Erasure Coded Pool and RBD block devices.

3 Ceph clients use the RBD devices, each has 25 RBDs  and Each RBD size is
10TB. Each RBD is partitioned with the EXT4 file system.

Cluster Health Is OK and Hardware is New and good.

All the machines have 10Gbps (Active/Passive) bond Interface  configured on
it.

Read operation of the cluster is OK, however, writes are very slow.

One one of the RBDs we did the perf test.

fio -ioengine=libaio -direct=1 -invalidate=1 -name=test -bs=4k -iodepth=128
-rw=randread -runtime=60 -filename=/dev/rbd40

Run status group 0 (all jobs):
   READ: bw=401MiB/s (420MB/s), 401MiB/s-401MiB/s (420MB/s-420MB/s),
io=23.5GiB (25.2GB), run=60054-60054msec

fio -ioengine=libaio -direct=1 -invalidate=1 -name=test -bs=4k -iodepth=128
-rw=randwrite -runtime=60 -filename=/dev/rbd40

Run status group 0 (all jobs):
  WRITE: bw=217KiB/s (222kB/s), 217KiB/s-217KiB/s (222kB/s-222kB/s),
io=13.2MiB (13.9MB), run=62430-62430msec

I see a High IO wait from the client.

Any suggestions/pointers address this issue is really appreciated.

Thanks and Regards,

Athreya
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