[c-nsp] 2 to 3% packet loss on single VLAN on LAG interface

[Frank Bulk]

Looking for some tribal knowledge from this group -- we have a Cisco 7609-S
running IOS 15.2(4)S5 with RSP720C's and DFC3C's on all our line cards.  We
have two WS-X6704-10GE cards that move around 7 Gbps (that's a total of in
and out) at peak times between their 7 active interfaces.  Some of those
Gbps are mirrored traffic.

What our customers are seeing and what we have confirmed is 2 to 3% ICMP
packet loss for traffic in a certain VLAN that flow in/out of the 10G
cross-card port channel facing a Brocade ICX6610 stack.  This is packet loss
pinging *through* the router, not ICMP traffic terminating hitting the
router.  

e.g. 
server--1G---Cisco7609==10G==VLAN A==Brocade---CPE  (packet loss)
server--1G---Cisco7609==10G==VLAN B==Brocade---CMTS (no packet loss)
server--1G---Cisco7609==1G===VLAN A==access-gear---CPE (no packet loss)
laptop==access gear==10G==VLAN A==Brocade---CPE (no packet loss)
laptop==access gear---CPE (no packet loss)

That VLAN has about 4500 to 5500 active MAC addresses.  We can ping an IP
address in that certain VLANs that flow in/out some other 1G port-channel on
a WS-X6748-GE-TX and there is no packet loss.  Some of other VLANs I've
tested that flow in/out of the 10G cross-card port channel also don't have
packet loss.

So what would cause (what appears to be) a certain VLAN to drop some traffic
when flowing across a 10G port-channel and not a 1G port-channel?  I know
the 6704 has some performance limitations -- how do I measure that on the
box?

Regards,

Frank Bulk