Hi Andrey! On 07/31/2012 10:03 AM, Andrey Korolyov wrote:
Hi, I`ve finally managed to run rbd-related test on relatively powerful machines and what I have got: 1) Reads on almost fair balanced cluster(eight nodes) did very well, utilizing almost all disk and bandwidth (dual gbit 802.3ad nics, sata disks beyond lsi sas 2108 with wt cache gave me ~1.6Gbyte/s on linear and sequential reads, which is close to overall disk throughput)
Does your 2108 have the RAID or JBOD firmware? I'm guessing the RAID firmware given that you are able to change the caching behavior? How do you have the arrays setup for the OSDs?
2) Writes get much worse, both on rados bench and on fio test when I ran fio simularly on 120 vms - at it best, overall performance is about 400Mbyte/s, using rados bench -t 12 on three host nodes fio config: rw=(randread|randwrite|seqread|seqwrite) size=256m direct=1 directory=/test numjobs=1 iodepth=12 group_reporting name=random-ead-direct bs=1M loops=12 for 120 vm set, Mbyte/s linear reads: MEAN: 14156 STDEV: 612.596 random reads: MEAN: 14128 STDEV: 911.789 linear writes: MEAN: 2956 STDEV: 283.165 random writes: MEAN: 2986 STDEV: 361.311 each node holds 15 vms and for 64M rbd cache all possible three states - wb, wt and no-cache has almost same numbers at the tests. I wonder if it possible to raise write/read ratio somehow. Seems that osd underutilize itself, e.g. I am not able to get single-threaded rbd write to get above 35Mb/s. Adding second osd on same disk only raising iowait time, but not benchmark results.
I've seen high IO wait times (especially with small writes) via rados bench as well. It's something we are actively investigating. Part of the issue with rados bench is that every single request is getting written to a seperate file, so especially at small IO sizes there is a lot of underlying filesystem metadata traffic. For us, this is happening on 9260 controllers with RAID firmware. I think we may see some improvement by switching to 2X08 cards with the JBOD (ie IT) firmware, but we haven't confirmed it yet.
We actually just purchased a variety of alternative RAID and SAS controllers to test with to see how universal this problem is. Theoretically RBD shouldn't suffer from this as badly as small writes to the same file should get buffered. The same is true for CephFS when doing buffered IO to a single file due to the Linux buffer cache. Small writes to many files will likely suffer in the same way that rados bench does though.
-- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
-- Mark Nelson Performance Engineer Inktank -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
