This took me a while to figure out, so I thought I'd quickly document it.
In our PE2850, we have a 'Dell PowerEdge Expandable RAID Controller 4e/Si'. To check the status of the disks, you'll need to fetch megarc from LSI. Download this file onto the server with the RAID card, and also download check_lsi_megaraid. You'll need to slightly modify check_lsi_megaraid , it prints out things like 'RAID OK:' and 'RAID WARNING:', change these to just say 'OK', and 'WARNING', and obviously update the others too. Notice there's no : in my version.
This script takes about 3 seconds to run, and should produce the following output.
# ./check_lsi_megaraid
OK All arrays OK [1 array checked on 1 controller]
I didn't want SNMP to block whlist waiting for this script to run, so I used cron to run it every minute, and throw it's output into a temp file. In /etc/crontab I have this:
* root /root/mega/check_lsi_megaraid > /tmp/raid-status
In snmpd.conf, I then put this:
extend raid-status /bin/cat /tmp/raid-status
Restart your snmpd server, and follow these instructions for configuring nagios.
See also: Monitoring Dell SAS 5iR RAID