I will assume you have a WS-X6148-GE-TX card. Then:
The WS-X6548-GE-TX, WS-X6548V-GE-TX, WS-X6148-GE-TX, and
WS-X6148V-GE-TX modules have a limitation with EtherChannel.
EtherChannel is supported on these modules for all configurations (10,
100, and 1000 Mbps speeds) but be aware of these cases of
oversubscription when you configure these modules:
On these modules there is a single 1-Gigabit Ethernet
uplink from the port ASIC that supports eight ports. For EtherChannel,
the data from all links in a bundle goes to the port ASIC, even though
the data is destined for another link. This data consumes bandwidth in
the 1-Gigabit Ethernet link. For these modules, the sum total of all
data on an EtherChannel cannot exceed 1 Gigabit.
You receive a message on the maximum throughput when you
add a port of this module to EtherChannel.
C6500> (enable) set port channel 3/5,4/5 mode on
Adding a WS-X6148-GE-TX port to a channel limits the channel's
bandwidth to a maximum of 1Gig throughput
--------------------------------------------------------
The 1 Gig restriction is a hardware limitation on the WS-X6148-GE-TX. If you
want 8 GE ports at line rate, then you will need to use a WS-X6748-GE-TX
(which requires Sup720). The WS-X6148-GE-TX, WS-X6548-GE-TX and
WS-X6148A-GE-TX are all 8:1 oversubscribed, meaning you will get no more
than 6-Gbps of bandwidth from any one of those linecards.
From the CatOS 8.x Release Notes :
The WS-X6548-GE-TX, WS-X6548V-GE-TX, WS-X6148-GE-TX, and WS-X6148V-GE-TX
modules do not support the following:
ÂMore than 1 Gbps of traffic per EtherChannel
********************************************** <<<<<<<<<<<<<<
Note With software release 8.2(1) [and newer], due to firmware enhancements,
the oversubscription problems associated with EtherChannel are no longer an
issue with the WS-X6548-GE-TX module.
********************************************** <<<<<<<<<<<<<<
This means that you can have let's say ports 1 and 9 on the WS-X6548-GE-TX working in a 2Gb channel after 8.2(1) or in IOS
