Hey, That sounds awful. Have you had any luck in increasing the performance?
Cheers, Josef Christian Balzer skrev 2014-05-23 17:57:
For what it's worth (very little in my case)... Since the cluster wasn't in production yet and Firefly (0.80.1) did hit Debian Jessie today I upgraded it. Big mistake... I did the recommended upgrade song and dance, MONs first, OSDs after that. Then applied "ceph osd crush tunables default" as per the update instructions and since "ceph -s" was whining about it. Lastly I did a "ceph osd pool set rbd hashpspool true" and after that was finished (people with either a big cluster or slow network probably should avoid this like the plague) I re-ran the below fio from a VM (old or new client libraries made no difference) again. The result, 2800 write IOPS instead of 3200 with Emperor. So much for improved latency and whatnot... Christian On Wed, 14 May 2014 21:33:06 +0900 Christian Balzer wrote:Hello! On Wed, 14 May 2014 11:29:47 +0200 Josef Johansson wrote:Hi Christian, I missed this thread, haven't been reading the list that well the last weeks. You already know my setup, since we discussed it in an earlier thread. I don't have a fast backing store, but I see the slow IOPS when doing randwrite inside the VM, with rbd cache. Still running dumpling here though.Nods, I do recall that thread.A thought struck me that I could test with a pool that consists of OSDs that have tempfs-based disks, think I have a bit more latency than your IPoIB but I've pushed 100k IOPS with the same network devices before. This would verify if the problem is with the journal disks. I'll also try to run the journal devices in tempfs as well, as it would test purely Ceph itself.That would be interesting indeed. Given what I've seen (with the journal at 20% utilization and the actual filestore ataround 5%) I'd expect Ceph to be the culprit.I'll get back to you with the results, hopefully I'll manage to get them done during this night.Looking forward to that. ^^ ChristianCheers, Josef On 13/05/14 11:03, Christian Balzer wrote:I'm clearly talking to myself, but whatever. For Greg, I've played with all the pertinent journal and filestore options and TCP nodelay, no changes at all. Is there anybody on this ML who's running a Ceph cluster with a fast network and FAST filestore, so like me with a big HW cache in front of a RAID/JBODs or using SSDs for final storage? If so, what results do you get out of the fio statement below per OSD? In my case with 4 OSDs and 3200 IOPS that's about 800 IOPS per OSD, which is of course vastly faster than the normal indvidual HDDs could do. So I'm wondering if I'm hitting some inherent limitation of how fast a single OSD (as in the software) can handle IOPS, given that everything else has been ruled out from where I stand. This would also explain why none of the option changes or the use of RBD caching has any measurable effect in the test case below. As in, a slow OSD aka single HDD with journal on the same disk would clearly benefit from even the small 32MB standard RBD cache, while in my test case the only time the caching becomes noticeable is if I increase the cache size to something larger than the test data size. ^o^ On the other hand if people here regularly get thousands or tens of thousands IOPS per OSD with the appropriate HW I'm stumped. Christian On Fri, 9 May 2014 11:01:26 +0900 Christian Balzer wrote:On Wed, 7 May 2014 22:13:53 -0700 Gregory Farnum wrote:Oh, I didn't notice that. I bet you aren't getting the expected throughput on the RAID array with OSD access patterns, and that's applying back pressure on the journal.In the a "picture" being worth a thousand words tradition, I give you this iostat -x output taken during a fio run: avg-cpu: %user %nice %system %iowait %steal %idle 50.82 0.00 19.43 0.17 0.00 29.58 Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await r_await w_await svctm %util sda 0.00 51.50 0.00 1633.50 0.00 7460.00 9.13 0.18 0.11 0.00 0.11 0.01 1.40 sdb 0.00 0.00 0.00 1240.50 0.00 5244.00 8.45 0.30 0.25 0.00 0.25 0.02 2.00 sdc 0.00 5.00 0.00 2468.50 0.00 13419.00 10.87 0.24 0.10 0.00 0.10 0.09 22.00 sdd 0.00 6.50 0.00 1913.00 0.00 10313.00 10.78 0.20 0.10 0.00 0.10 0.09 16.60 The %user CPU utilization is pretty much entirely the 2 OSD processes, note the nearly complete absence of iowait. sda and sdb are the OSDs RAIDs, sdc and sdd are the journal SSDs. Look at these numbers, the lack of queues, the low wait and service times (this is in ms) plus overall utilization. The only conclusion I can draw from these numbers and the network results below is that the latency happens within the OSD processes. Regards, ChristianWhen I suggested other tests, I meant with and without Ceph. One particular one is OSD bench. That should be interesting to try at a variety of block sizes. You could also try runnin RADOS bench and smalliobench at a few different sizes. -Greg On Wednesday, May 7, 2014, Alexandre DERUMIER <aderum...@odiso.com> wrote:Hi Christian, Do you have tried without raid6, to have more osd ? (how many disks do you have begin the raid6 ?) Aslo, I known that direct ios can be quite slow with ceph, maybe can you try without --direct=1 and also enable rbd_cache ceph.conf [client] rbd cache = true ----- Mail original ----- De: "Christian Balzer" <ch...@gol.com <javascript:;>> À: "Gregory Farnum" <g...@inktank.com <javascript:;>>, ceph-users@lists.ceph.com <javascript:;> Envoyé: Jeudi 8 Mai 2014 04:49:16 Objet: Re: [ceph-users] Slow IOPS on RBD compared to journal and backing devices On Wed, 7 May 2014 18:37:48 -0700 Gregory Farnum wrote:On Wed, May 7, 2014 at 5:57 PM, Christian Balzer <ch...@gol.com<javascript:;>>wrote:Hello, ceph 0.72 on Debian Jessie, 2 storage nodes with 2 OSDs each. The journals are on (separate) DC 3700s, the actual OSDs are RAID6 behind an Areca 1882 with 4GB of cache. Running this fio: fio --size=400m --ioengine=libaio --invalidate=1 --direct=1 --numjobs=1 --rw=randwrite --name=fiojob --blocksize=4k --iodepth=128 results in: 30k IOPS on the journal SSD (as expected) 110k IOPS on the OSD (it fits neatly into the cache, no surprise there) 3200 IOPS from a VM using userspace RBD 2900 IOPS from a host kernelspace mounted RBD When running the fio from the VM RBD the utilization of the journals is about 20% (2400 IOPS) and the OSDs are bored at 2% (1500 IOPS after some obvious merging). The OSD processes are quite busy, reading well over 200% on atop, but the system is not CPU or otherwise resource starved at that moment. Running multiple instances of this test from several VMs on different hosts changes nothing, as in the aggregated IOPS for the whole cluster will still be around 3200 IOPS. Now clearly RBD has to deal with latency here, but the network is IPoIB with the associated low latency and the journal SSDs are the (consistently) fasted ones around. I guess what I am wondering about is if this is normal and to be expected or if not where all that potential performance got lost.Hmm, with 128 IOs at a time (I believe I'm reading that correctly?)Yes, but going down to 32 doesn't change things one iota. Also note the multiple instances I mention up there, so that would be 256 IOs at a time, coming from different hosts over different links and nothing changes.that's about 40ms of latency per op (for userspace RBD), which seems awfully long. You should check what your client-side objecter settings are; it might be limiting you to fewer outstanding ops than that.Googling for client-side objecter gives a few hits on ceph devel and bugs and nothing at all as far as configuration options are concerned. Care to enlighten me where one can find those? Also note the kernelspace (3.13 if it matters) speed, which is very much in the same (junior league) ballpark.If it's available to you, testing with Firefly or even master would be interesting — there's some performance work that should reduce latencies.Not an option, this is going into production next week.But a well-tuned (or even default-tuned, I thought) Ceph cluster certainly doesn't require 40ms/op, so you should probably run a wider array of experiments to try and figure out where it's coming from.I think we can rule out the network, NPtcp gives me: --- 56: 4096 bytes 1546 times --> 979.22 Mbps in 31.91 usec --- For comparison at about 512KB it reaches maximum throughput and still isn't that laggy: --- 98: 524288 bytes 121 times --> 9700.57 Mbps in 412.35 usec --- So with the network performing as well as my lengthy experience with IPoIB led me to believe, what else is there to look at? The storage nodes perform just as expected, indicated by the local fio tests. That pretty much leaves only Ceph/RBD to look at and I'm not really sure what experiments I should run on that. ^o^ Regards, Christian-Greg Software Engineer #42 @ http://inktank.com | http://ceph.com-- Christian Balzer Network/Systems Engineer ch...@gol.com <javascript:;> Global OnLine Japan/Fusion Communications http://www.gol.com/ _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com <javascript:;> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com_______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
_______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
