[ceph-users] Re: Understanding op_r, op_w vs op_rw

I did say I'd test using librbd - and this changes my observations. Using fio configured with the rbd driver: - a random write workload emits about equal 'op_w' and 'op_rw' initially, then just 'op_w' (until filled in sparse allocation maybe)? So this certainly does help me understand why I'm seeing a lot of 'op_rw', but any further clarification appreciated! regards Mark On 2/09/20 6:17 pm, Mark Kirkwood wrote: > Hi, > > I'd like to gain a better understanding about what operations emit > which of these performance counters, in particular when is 'op_rw' > incremented instead of 'op_r' + 'op_w'? > > I've done a little bit of investigation (v12.2.13) , running various > workoads and operations against an RBD volume (in a cluster with no > other client activity): > > - Most RBD 'operations'  (create, rm, features disable/enable, map, > unmap) emit 'op_rw' and often 'op_w' too > > - Program reads and writes against a mounted RBD volume *only* emit > 'op_r' and 'op_w' (never 'op_rw'), regardless of whether they are > 'read + modify' of existing file data (or whether the writes are > buffered, direct or sync) > > Is that correct? Or have I missed a program driven workload that will > produce 'op_rw'? [1] > > In our production clusters I'm seeing similar numbers of 'op_w' and > 'op_rw' (for a given OSD), which would suggest a lot of RBD operations > if it is only them that cause 'op_rw' counters to be emitted. > > Cheers > > Mark > > [1] Tested using fio and pgbench (database benchmark). I mounted the > volume using the kernel driver (I'll do some more experimentation > using librbd) > > _______________________________________________ > ceph-users mailing list -- ceph-users(a)ceph.io > To unsubscribe send an email to ceph-users-leave(a)ceph.io