We have recently installed a UCS enviornment with 2 x 6100 units connected to our dual 6509 core. It is set up so that 2 x 10GigE uplinks connect from FAB-A to 6509-1 and 2 x 10GigE connect from FAB-B to 6509-2. Each of the 4 trunks to the 6509 enviorment are configured the same and truck the same 4 VLAN to FAB-A or FAB-B. We have 2 x UCS Chassis, each with 4 half-width servers. Each chassis has an A and B side, with 20GB going to FAB-A and 20GB going FAB-B.
The above UCS enviorment was installed by a 3rd party, while I configured the core-side of the links.
Our server team recently brought up a Windows server and I started seeing mac-flapping on one of our cores, between one of the 10GigE ports connected to FAB-A and the trunk link that exists between our 2 cores.
I'm a bit unsure about how, on the 6509 side, the ports should be configured.. I was told by the 3rd party that there is no 'active/standby' design, all of the trunks to each of the two 6100s are active 'all the time'. Our 6509 aren't running the VSS supervisors, just 'standard' sup720s running HSRP, with a trunk between the two.
I understand that more details is probably required, but I said i'd look into from a networking/core standpoint and the server guy is checking out his end, as as it stands he has the server in question connected to 2 vNICs, one on each of the 6100s, both 'up'.
Looking at the thread, it mentions of a vswitch.
For hypervisor based environments, (currently) the recommendation is to have Fabric Failover OFF and Brad's blog indicates that.
So turning on Fabric failover will not do you any good and will have unpredictable failover when failure occurs.
A detailed topology (or a TAC case) would be useful to narrow down on the issue.
A lot depends on how your vswitch is configured as before the traffic hits either of the FI's, the vswitch has to make a forwarding decision which side to go out - on A or B (give you have 2 vNICs given to a vswitch which I believe you would have). Once the traffic comes to a particular FI, then again it depends on which active uplink it will take which could dictate if the trunk between the cores get used etc.
Hope that helps.