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10gbit performance tuning - win2k8r2 server on 6509


this is my szenario:

4x  catalyst 6509 with sup720 and a X6704-10GE Module each, which are connected with 10gbit links in a circle. So its 2 ports per c6509 for the backbone.

on every 6509 Switch we connected one Server on the same module with a 10gbit sfp+ NIC. (Servers are for main backup and the only ones with 10gbit NICs so far)

now we have tested network performance / throughput with iperf. i dont know if iperf is qualified to test 10gbit connections, but the backup solution vendor also used it and has very good results (about 980 MByte/s) with these parameters: iperf -c hostname -P 4 -w 262144 -f MByte.

With the same parameters i only reach about ~100 to 130 MByte/s which is actually only a little over 1 GBit/s. RTT between the servers is <1ms of course and a bigger window size did not help either.

load of the 10gig-backbone links is not very high, not reaching more than 1gbit/s most of the time, currently:

5 minute input rate 370.963.000 bits/sec, 63384 packets/sec

5 minute output rate 486.548.000 bits/sec, 69451 packets/sec

a.) does anyone know where there could be a problem?

b.) does anyone know a good tool for high performance throughput testing other than iperf? (free / open source if possible)

c.) windows 2008 R2 has a "Next generation TCP/IP Stack" with auto-tuning, so there are no custom configurable settings like TCP window size etc anymore... is there anything else to configure?

d.) the Server NICs would support jumbo frames (MTU 9000+), i assume there would be a benefit if the servers communicate with their maxium paketsize with each other? all devices between them supports that, and connections to other servers would still work with MTU 1500 because of PMTU discovery, am i right? is there anything else to set on the 6509 except mtu 9216 on the interface? actually i will have to set that MTU on all 10gbit interfaces then, could that lead into problems for the rest of my network?

thanks for your thoughts and hints,

brgds Roland

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