[OpenAFS] Windows client network behaviour

Anders Magnusson ragge@ltu.se
Wed, 21 Sep 2011 13:09:26 +0200

In the hunt for oddities regarding the new IFS Windows client I have 
observed a problem causing bad performance, and hopefully someone has 
some idea about what is going on.

Server:  OpenAFS, CentOS 5.3
Client: Windows 7, OpenAFS 1.7.1

The test case is to write an ISO image (700MB) to afs from local disk.

If the switch port is set to 100Mbit I will get ~3Mbyte/s, but if it is 
set to 1Gbit then I get ~10Mbyte/s.
Both these numbers are much lower than they should be, and more 
precisely I cannot understand why the speed in 100Mbit configuration 
becomes much lower than when using 1Gbit.

Before someone asks; there are no network limits here and both client 
and server are on the same subnet.

I have run tcpdump on both client and server and seen this traffic 

For 100Mbit:
- A data packet is sent out periodically at an almost exact rate of one 
1472 byte
   per 420 microseconds, which gives something close to 3Mbyte/s

For 1Gbit:
- The same as for 100Mbit except for that the packet rate is one packet 
per 91 microseconds.

The ack packet from the file server is sent back 12 microseconds after 
each second data packet.

I have uninstalled the QoS module on the Windows interface.

Any hints anyone? I think this smells as traffic shaping due to the 
quite exact transmit rate but
since the QoS module is uninstalled and the behaviour is seen on the 
windows network interface
I have no clue where it may be.

A side note: Going via a SMB-AFS gateway on the same network gives 
significantly better

-- Ragge