[OpenAFS] Expected performance

[Hugo Monteiro]

Hello all,

We have a 1.4.12 openafs server, which is a VM sitting on a SAN storage 
(Xen based Oracle VM), having 2GB of ram and 4 vcpus.
After some test runs, we were a bit displeased with the obtained 
transfer rate.
Tests were made using dd, with files greater than the client cache size 
forcing a sync after dd ended. (roughly what's observed here 
http://it.toolbox.com/blogs/database-soup/testing-disk-speed-the-dd-test-31069). 
Each test was performed in equal situation, with no concurrent access, 
and each system was only performing the test at that time.

- Low performance and high discrepancy between test results
Transfer rates (only a few) hardly touched 30MB/s between the server and 
a client sitting on the same network, connected via GB ethernet. Most of 
the times that transfer rate is around 20MB/s, falling down to 13 or 
14MB/s in some cases.

- Problem doesn't seem to be network related
After these findings, we then performed exactly the same tests on the 
server machine, while acting as client of itself, i.e. with no physical 
network involved. The outcome, sadly, was the same. We tried both with 
and without jumbograms and we obtained roughly the same results, either 
while using 2 machines (client/server) or only one machine.

- No concerning system load
We observed no major cpu activity, having fileserver reach around 30% of 
cpu usage in some very short peaks. Memory was also fine all through the 
tests.

- It's not the disks either
We also outruled disk bottleneck since on the same machines, using the 
exact same type of storage we would get around 130MB/s while reading and 
110MB/s while writing.
Another very weird thing was that reading transfers were (mostly) all 
slower than writting.


Does anyone detect any kind of inconsistency in this scenario or were 
our expectations a bit too high?

Best regards,

Hugo Monteiro.

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Hugo Monteiro
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