Are you seeing errors like the following?
SYS-3-SYS_RMONMEMLOW:Fail to allocate memory for RMON. System
memory usage excess 85%
The default RMONmemory allocated is 85% and is configurable
http://cio.cisco.com/univercd/cc/td/doc/product/lan/cat6000/sw_6_3/cmd_ref/setsn_su.htm#50850
But these errors are likely being caused by one of 3 things
1) insufficient memory for features/utilization
2) memory leak..Take a look at the following bug
http://www.cisco.com/cgi-bin/bugtool/onebug.pl?bugid=CSCdx19098
3) Rmon config conditions
Basically, there is a memory limit on all of our switches as far as how many buckets can be allocated for short and long term history (ie not capable for all ports). Therefore you will get the error that you are running into if you are
getting buckets for history on too many ports. This is outlined in the doc
below...and in the command guides for the switches.
http://www.cisco.com/warp/public/701/25.html
With respect to RMON, because you are using a switch and not a switch probe you will only be able to collect mini- RMON stats. This includes alarms
and events and you can configure as seen in the following links:
Configuring Alarms:
http://www.cisco.com/univercd/cc/td/doc/product/rtrmgmt/sw_ntman/td_main/td_5_6/traf5_6/alarms.htm
Mini-RMON
http://www.cisco.com/univercd/cc/td/doc/product/rtrmgmt/sw_ntman/td_main/td_5_6/traf5_6/switches.htm
