We recently needed to reweight a couple of OSDs on one of our clusters
(luminous on Ubuntu, 8 hosts, 8 OSD/host). I (think) we reweighted by
approx 0.2. This was perhaps too much, as IO latency on RBD drives
spiked to several seconds at times.
We'd like to lessen this effect as much as we can. So we are looking at
priority and queue parameters (OSDs are Filestore based with S3700 SSD
or similar NVME journals):
# priorities
osd_client_op_priority
osd_recovery_op_priority
osd_recovery_priority
osd_scrub_priority
osd_snap_trim_priority
# queue tuning
filestore_queue_max_ops
filestore_queue_low_threshhold
filestore_queue_high_threshhold
filestore_expected_throughput_ops
filestore_queue_high_delay_multiple
filestore_queue_max_delay_multiple
My first question is this - do these parameters require the CFQ
scheduler (like osd_disk_thread_ioprio_priority does)? We are currently
using deadline (we have not tweaked queue/iosched/write_expire down from
5000 to 1500 which might be good to do).
My 2nd question is - should we consider increasing
osd_disk_thread_ioprio_priority (and hence changing to CFQ scheduler)? I
usually see this parameter discussed WRT scrubbing, and we are not
having issues with that.
regards
Mark
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