On 09/10/2012 03:15 PM, Mike Ryan wrote:
*Disclaimer*: these results are an investigation into potential
bottlenecks in RADOS. The test setup is wholly unrealistic, and these
numbers SHOULD NOT be used as an indication of the performance of OSDs,
messaging, RADOS, or ceph in general.
Executive summary: rados bench has some internal bottleneck. Once that's
cleared up, we're still having some issues saturating a single
connection to an OSD. Having 2-3 connection in parallel alleviates that
(either by having> 1 OSD or having multiple bencher clients).
I've run three separate tests: msbench, smalliobench, and rados bench.
In all cases I was trying to determine where bottleneck(s) exist. All
the tests were run on a machine with 192 GB of RAM. The backing stores
for all OSDs and journals are RAMdisks. The stores are running XFS.
smalliobench: I ran tests varying the number of OSDs and bencher
clients. In all cases, the number of PG's per OSD is 100.
OSD Bencher Throughput (mbyte/sec)
1 1 510
1 2 800
1 3 850
2 1 640
2 2 660
2 3 670
3 1 780
3 2 820
3 3 870
4 1 850
4 2 970
4 3 990
Note: these numbers are fairly fuzzy. I eyeballed them and they're only
really accurate to about 10 mbyte/sec. The small IO bencher was run with
100 ops in flight, 4 mbyte io's, 4 mbyte files.
msbench: ran tests trying to determine max throughput of raw messaging
layer. Varied the number of concurrently connected msbench clients and
measured aggregate throughput. Take-away: a messaging client can very
consistently push 400-500 mbytes/sec through a single socket.
Clients Throughput (mbyte/sec)
1 520
2 880
3 1300
4 1900
Finally, rados bench, which seems to have its own bottleneck. Running
varying numbers of these, each client seems to get 250 mbyte/sec up till
the aggregate rate is around 1000 mbyte/sec (appx line speed as measured
by iperf). These were run on a pool with 100 PGs/OSD.
Clients Throughput (mbyte/sec)
1 250
2 500
3 750
4 1000 (very fuzzy, probably 1000 +/- 75)
5 1000, seems to level out here
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Hi guys,
Some background on all of this:
We've been doing some performance testing at Inktank and noticed that
performance with a single rados bench instance was plateauing at between
600-700MB/s. Running multiple concurrent rados bench instances improves
performance, but only to a certain extent. The fastest throughput we've
seen so far is around 1160MB/s with 8 rados bench instances, 12 spinning
disks, and journals on SSDs. This is true regardless of the underlying
filesystem on the OSDs, though some hit the limits faster than others.
Some of the raw data is available here:
https://docs.google.com/a/inktank.com/spreadsheet/ccc?key=0AnmmfpoQ1_94dDlmTHhvM19zd19tb05zbFVqZ2xSYXc#gid=0
To understand why we are plateauing, we wanted to investigate what
bottlenecks were present in rados bench and if there also were any
bottlenecks in the messenger code that might be limiting throughput.
Soon we should have a 36 drive setup in our SC847a chassis where we can
try to push things even further. :)
Mark
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