Your 8k-block dd test is not nearly the same as your 8k-block rados bench or SQL tests. Both rados bench and SQL require the write to be committed to disk before moving on to the next one; dd is simply writing into the page cache. So you're not going to get 460 or even 273MB/s with sync 8k writes regardless of your settings.
However, I think you should be able to tune your OSDs into somewhat better numbers -- that rados bench is giving you ~300IOPs on every OSD (with a small pipeline!), and an SSD-based daemon should be going faster. What kind of logging are you running with and what configs have you set? Hopefully you can get Mark or Sam or somebody who's done some performance tuning to offer some tips as well. :) -Greg On Tuesday, September 17, 2013, Jason Villalta wrote: > Hello all, > I am new to the list. > > I have a single machines setup for testing Ceph. It has a dual proc 6 > cores(12core total) for CPU and 128GB of RAM. I also have 3 Intel 520 > 240GB SSDs and an OSD setup on each disk with the OSD and Journal in > separate partitions formatted with ext4. > > My goal here is to prove just how fast Ceph can go and what kind of > performance to expect when using it as a back-end storage for virtual > machines mostly windows. I would also like to try to understand how it > will scale IO by removing one disk of the three and doing the benchmark > tests. But that is secondary. So far here are my results. I am aware > this is all sequential, I just want to know how fast it can go. > > DD IO test of SSD disks: I am testing 8K blocks since that is the default > block size of windows. > dd of=ddbenchfile if=/dev/zero bs=8K count=1000000 > 8192000000 bytes (8.2 GB) copied, 17.7953 s, 460 MB/s > > dd if=ddbenchfile of=/dev/null bs=8K > 8192000000 bytes (8.2 GB) copied, 2.94287 s, 2.8 GB/s > > RADOS bench test with 3 SSD disks and 4MB object size(Default): > rados --no-cleanup bench -p pbench 30 write > Total writes made: 2061 > Write size: 4194304 > Bandwidth (MB/sec): 273.004 > > Stddev Bandwidth: 67.5237 > Max bandwidth (MB/sec): 352 > Min bandwidth (MB/sec): 0 > Average Latency: 0.234199 > Stddev Latency: 0.130874 > Max latency: 0.867119 > Min latency: 0.039318 > ----- > rados bench -p pbench 30 seq > Total reads made: 2061 > Read size: 4194304 > Bandwidth (MB/sec): 956.466 > > Average Latency: 0.0666347 > Max latency: 0.208986 > Min latency: 0.011625 > > This all looks like I would expect from using three disks. The problems > appear to come with the 8K blocks/object size. > > RADOS bench test with 3 SSD disks and 8K object size(8K blocks): > rados --no-cleanup bench -b 8192 -p pbench 30 write > Total writes made: 13770 > Write size: 8192 > Bandwidth (MB/sec): 3.581 > > Stddev Bandwidth: 1.04405 > Max bandwidth (MB/sec): 6.19531 > Min bandwidth (MB/sec): 0 > Average Latency: 0.0348977 > Stddev Latency: 0.0349212 > Max latency: 0.326429 > Min latency: 0.0019 > ------ > rados bench -b 8192 -p pbench 30 seq > Total reads made: 13770 > Read size: 8192 > Bandwidth (MB/sec): 52.573 > > Average Latency: 0.00237483 > Max latency: 0.006783 > Min latency: 0.000521 > > So are these performance correct or is this something I missed with the > testing procedure? The RADOS bench number with 8K block size are the same > we see when testing performance in an VM with SQLIO. Does anyone know of > any configure changes that are needed to get the Ceph performance closer to > native performance with 8K blocks? > > Thanks in advance. > > > > -- > -- > *Jason Villalta* > Co-founder > [image: Inline image 1] > 800.799.4407x1230 | www.RubixTechnology.com<http://www.rubixtechnology.com/> > -- Software Engineer #42 @ http://inktank.com | http://ceph.com
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