Hi Dave, The main line in SSD specs you should look at is
Enhanced Power Loss Data Protection: Yes
This makes SSD cache nonvolatile and makes SSD ignore fsync()s so transactional performance becomes equal to non-transactional. So your SSDs should be OK for journal.
rados bench is a bad tool for testing because of 4M default block size and a very small number of objects created for testing. Better test it with fio -ioengine=rbd -bs=4k -rw=randwrite and -sync=1 -iodepth=1 for latency or -iodepth=128 for max random load.
Another recent thing that I've discovered was that turning off write cache for all drives (for i in /dev/sd*; do hdparm -W 0 $i; done) increased write iops by an order of magnitude.
Hi all, We want to compare the performance between HDD partition as the journal (inline from OSD disk) and SSD partition as the journal, here is what we have done, we have 3 nodes used as Ceph OSD, each has 3 OSD on it. Firstly, we created the OSD with journal from OSD partition, and run "rados bench" utility to test the performance, and then migrate the journal from HDD to SSD (Intel S4500) and run "rados bench" again, the expected result is SSD partition should be much better than HDD, but the result shows us there is nearly no change, The configuration of Ceph is as below, pool size: 3 osd size: 3*3 pg (pgp) num: 300 osd nodes are separated across three different nodes rbd image size: 10G (10240M) The utility I used is, rados bench -p rbd $duration write rados bench -p rbd $duration seq rados bench -p rbd $duration rand Is there anything wrong from what I did? Could anyone give me some suggestion? Best Regards, Dave Chen _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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