>-----Original Message----- >From: Gregory Farnum [mailto:g...@inktank.com] >Sent: Tuesday, February 04, 2014 9:46 AM >To: Gruher, Joseph R >Cc: Mark Nelson; ceph-users@lists.ceph.com; Ilya Dryomov >Subject: Re: [ceph-users] Low RBD Performance > >On Tue, Feb 4, 2014 at 9:29 AM, Gruher, Joseph R ><joseph.r.gru...@intel.com> wrote: >> >> >>>-----Original Message----- >>>From: ceph-users-boun...@lists.ceph.com [mailto:ceph-users- >>>boun...@lists.ceph.com] On Behalf Of Mark Nelson >>>Sent: Monday, February 03, 2014 6:48 PM >>>To: ceph-users@lists.ceph.com >>>Subject: Re: [ceph-users] Low RBD Performance >>> >>>On 02/03/2014 07:29 PM, Gruher, Joseph R wrote: >>>> Hi folks- >>>> >>>> I'm having trouble demonstrating reasonable performance of RBDs. >>>> I'm running Ceph 0.72.2 on Ubuntu 13.04 with the 3.12 kernel. I >>>> have four dual-Xeon servers, each with 24GB RAM, and an Intel 320 >>>> SSD for journals and four WD 10K RPM SAS drives for OSDs, all >>>> connected with an LSI 1078. This is just a lab experiment using >>>> scrounged hardware so everything isn't sized to be a Ceph cluster, >>>> it's just what I have lying around, but I should have more than >>>> enough CPU and memory >>>resources. >>>> Everything is connected with a single 10GbE. >>>> >>>> When testing with RBDs from four clients (also running Ubuntu 13.04 >>>> with >>>> 3.12 kernel) I am having trouble breaking 300 IOPS on a 4KB random >>>> read or write workload (cephx set to none, replication set to one). >>>> IO is generated using FIO from four clients, each hosting a single >>>> 1TB RBD, and I've experimented with queue depths and increasing the >>>> number of RBDs without any benefit. 300 IOPS for a pool of 16 10K >>>> RPM HDDs seems quite low, not to mention the journal should provide >>>> a good boost on write workloads. When I run a 4KB object write >>>> workload in Cosbench I can approach 3500 Obj/Sec which seems more >reasonable. >>>> >>>> Sample FIO configuration: >>>> >>>> [global] >>>> >>>> ioengine=libaio >>>> >>>> direct=1 >>>> >>>> ramp_time=300 >>>> >>>> runtime=300 >>>> >>>> [4k-rw] >>>> >>>> description=4k-rw >>>> >>>> filename=/dev/rbd1 >>>> >>>> rw=randwrite >>>> >>>> bs=4k >>>> >>>> stonewall >>>> >>>> I use --iodepth=X on the FIO command line to set the queue depth >>>> when testing. >>>> >>>> I notice in the FIO output despite the iodepth setting it seems to >>>> be reporting an IO depth of only 1, which would certainly help >>>> explain poor performance, but I'm at a loss as to why, I wonder if >>>> it could be something specific to RBD behavior, like I need to use a >>>> different IO engine to establish queue depth. >>>> >>>> IO depths : 1=200.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >>>>=64=0.0% >>>> >>>> Any thoughts appreciated! >>> >>>Interesting results with the io depth at 1. I Haven't seen that >>>behaviour when using libaio, direct=1, and higher io depths. Is this kernel >RBD or QEMU/KVM? >>>If it's QEMU/KVM, is it the libvirt driver? >>> >>>Certainly 300 IOPS is low for that kind of setup compared to what >>>we've seen for RBD on other systems (especially with 1x replication). >>>Given that you are seeing more reasonable performance with RGW, I >>>guess I'd look at a couple >>>things: >>> >>>- Figure out why fio is reporting queue depth = 1 >> >> Yup, I agree, I will work on this and report back. First thought is to try >specifying the queue depth in the FIO workload file instead of on the >command line. >> >>>- Does increasing the num jobs help (ie get concurrency another way)? >> >> I will give this a shot. >> >>>- Do you have enough PGs in the RBD pool? >> >> I should, for 16 OSDs and no replication I use 2048 PGs/PGPs (100 * 16 / 1 >rounded up to power of 2). >> >>>- Are you using the virtio driver if QEMU/KVM? >> >> No virtualization, clients are bare metal using kernel RBD. > >I believe that directIO via the kernel client will go all the way to the OSDs >and >to disk before returning. I imagine that something in the stack is preventing >the dispatch from actually happening asynchronously in that case, and the >reason you're getting 300 IOPS is because your total RTT is about 3 ms with >that code... > >Ilya, is that assumption of mine correct? One thing that occurs to me is that >for >direct IO it's fair to use the ack instead of on-disk response from the OSDs, >although that would only help us for people using btrfs. >-Greg >Software Engineer #42 @ http://inktank.com | http://ceph.com
Ultimately this seems to be an FIO issue. If I use "--iodepth X" or "--iodepth=X" on the FIO command line I always get queue depth 1. After switching to specifying "iodepth=X" in the body of the FIO workload file I do get the desired queue depth and I can immediately see performance is much higher (a full re-test is underway, I can share some results when complete if anyone is curious). This seems to have effectively worked around the problem, although I'm still curious why the command line parameters don't have the desired effect. Thanks for the responses! _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
