Lowering Ceph scrub I/O priority [feedly]

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Lowering Ceph scrub I/O priority
// Ceph

The disk I/O of a Ceph OSD thread scrubbing is the same as all other threads by default. It can be lowered with ioprio options for all OSDs with:

ceph tell osd.* injectargs '--osd_disk_thread_ioprio_priority 7'  ceph tell osd.* injectargs '--osd_disk_thread_ioprio_class idle'  

All other threads in the OSD will be be (best effort) with priority 4 which is the default for daemons. The disk thread will show as idle:

$ sudo iotop --batch --iter 1 | grep 'ceph-osd -i 0' | grep -v be/4   4156 idle loic        0.00 B/s    0.00 B/s  0.00 %  0.00 % ./ceph-osd -i 0 ..  

The change will only be effective if the scheduler is cfq (it can safely be modified at runtime)

# cat /sys/block/sda/queue/scheduler  noop [deadline] cfq  # echo cfq > /sys/block/sda/queue/scheduler  

To display the current value for a given OSD the following can be run from the host on which it is running (because it uses the asok file found in /var/run/ceph):

$ ceph daemon osd.0 config get osd_disk_thread_ioprio_class  { "osd_disk_thread_ioprio_class": "idle"}  $ ceph daemon osd.0 config get osd_disk_thread_ioprio_priority  { "osd_disk_thread_ioprio_priority": "7"}  

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