I'm running some tests with mixed storage units, and octopus. 8 nodes, each with 2 SSDs, and 8 HDDs . the SSDsare relatively small: around 100GB each. Im mapping 8 rbds, striping them together, and running fio on them for testing. # fio --filename=/...../fio.testfile --size=120GB --rw=randrw --bs=8k --direct=1 --ioengine=libaio --iodepth=64 --numjobs=4 --time_based --group_reporting --name=readwritelatency-test-job --runtime=120 --eta-newline=1 Trouble is, I'm seeing sporadic delays of IOs. When I test ZFS, for example, it has this neat wait clumping status check: zpool iostat -w 20 and it shows me that some write io's are taking over 4 secomds to complete. Many are taking 1s or 2s This kind of thing has sort of happened before(but previously, I think I was using SSDs exclusively). When I emailed the list, people suggested turning off RBD cache, which worked great in that situation. This time, I have already done that (I believe), but still see this behavior. Would folks have any further suggestions to smooth performance out? The odd thing is, I read that bluestore is supposed to smooth things out and provide consistent response time, but that doesnt seem to be the case. Sample output from the zpool iostat below: twelve total_wait disk_wait syncq_wait asyncq_wait latency read write read write read write read write scrub trim ---------- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- .. snip ... 1ms 1.01K 0 1.00K 0 0 0 0 0 0 0 2ms 29 0 29 18 0 0 0 1 0 0 4ms 23 3 23 14 0 0 0 3 0 0 8ms 64 6 64 9 0 0 0 7 0 0 16ms 74 10 74 59 0 0 0 11 0 0 33ms 24 17 24 154 0 0 0 19 0 0 67ms 7 25 7 100 0 0 0 26 0 0 134ms 3 40 3 36 0 0 0 36 0 0 268ms 1 59 1 18 0 0 0 59 0 0 536ms 0 116 0 3 0 0 0 113 0 0 1s 0 109 0 0 0 0 0 98 0 0 2s 0 24 0 0 0 0 0 20 0 0 4s 0 2 0 0 0 0 0 1 0 0 8s 0 0 0 0 0 0 0 0 0 0 17s 0 0 0 0 0 0 0 0 0 0 -- Philip Brown| Sr. Linux System Administrator | Medata, Inc. 5 Peters Canyon Rd Suite 250 Irvine CA 92606 Office 714.918.1310| Fax 714.918.1325 pbrown@medata.com| www.medata.com