I have a strange LAN problem concerning the varying/erratic response times of servers connected to a C6500 switch.
The network consists of 2 C6500 core switches and 10 C3750 stacks (about 600 ports). The C6500 core switches are interconnected via 1 fibre link, the stacks are connected to the C6500 via fiber links ether-channels (each stack to 1 C6500 only). The users (cca 600) are connected to the C3750s and servers (cca 20) are connected to the C6500s. There are several VLANs configured. Almost everything works fine, but about 10 servers have variably slow response times. The ping response time to the servers varies from 1ms to 1000ms (intra or inter VLAN). When I have simultaneously pinged a couple of servers, the response time increased for all of them in the same moment.
I have moved 2 servers to other module/interface and they are working fine (constant response time max 5ms). I have moved another 1-2 servers to other module/interface and for these servers the problem is still there.
I'm not able to assign the problem to individual servers, nor individual modules/interfaces on the switch. Most of the servers are connected via 2+ NICs. The LAN infrastructure has been 3COM before and they didn't have such problem.
I have no clue what could be the reason for such behaviour, so I'm thankful for any idea.