Nagios monitoring ReadyNAS via SNMP

First up: the ReadyNAS does have an SNMP implementation, but it's off by default, so go turn it on: Front Panel -> System -> Alerts, select the SNMP tab.

Test it works:

$ snmpwalk -v1 -cpublic my-nas-box-ip
SNMPv2-MIB::sysDescr.0 = STRING: Linux my-nas-box 2.6.17.8ReadyNAS #1 Tue Jun 9 13:59:28 PDT 2009 padre

[buckets of usual SNMP output omitted]

The interesting stuff is found here:
$ snmpwalk -v1 -cpublic my-nas-box-ip enterprises.4526
SNMPv2-SMI::enterprises.4526.18.1.0 = STRING: "4.01c1-p6"

[smaller buckets of output omitted]

$ snmpwalk -v1 -cpublic my-nas-box-ip enterprises.4526.18.7
SNMPv2-SMI::enterprises.4526.18.7.1.1.1 = INTEGER: 1
SNMPv2-SMI::enterprises.4526.18.7.1.2.1 = STRING: "Volume C"
SNMPv2-SMI::enterprises.4526.18.7.1.3.1 = STRING: " RAID Level X"
SNMPv2-SMI::enterprises.4526.18.7.1.4.1 = STRING: "ok"
SNMPv2-SMI::enterprises.4526.18.7.1.5.1 = INTEGER: 4262912
SNMPv2-SMI::enterprises.4526.18.7.1.6.1 = INTEGER: 3679876

These items are the (RAID) volume table:
1 is the first RAID volume (and indeed my only one)
Volume C is the name of the RAID volume - it's the default ReadyNAS one
RAID Level X means we're using the ReadyNAS default X-RAID
ok is the status of the volume - it's OK. Phew!
4262912 is the size in megabytes of the volume (I can't really make that tally against the actual size, I'm still puzzling over that one)
3679876 is the free space of the volume in megabytes

You can get the whole MIB here. There are plenty of other interesting things you can monitor, such as temp and fan speeds, but since we've set up email alerts if there are problems with those, I'm happy to leave them out of Nagios.

Now to set up Nagios:
Grab check_readynas_hd.pl from these guys. It only monitors RAID volume, and only the first one - that's all I wanted to monitor, so it's perfect. The code is nice and simple, so it'd be easy enough to expand it to cater for multiple volumes, maybe monitor temperatures, physical disks, if you were that way inclined. I found that the script assumed snmpwalk would be at /usr/bin/snmpwalk - not so for FreeBSD, but it wasn't too hard to hack it in as /usr/local/bin/snmpwalk

You also need the ReadyNAS MIB, so download that.

Running the script was easy:
$ /usr/local/libexec/nagios/check_readynas -H my-nas-box-ip -m /usr/local/libexec/nagios/READYNAS-MIB.txt
Volume C(RAID Level X): 4262912/3679876bytes (13% in use) STATUS: "ok"

Yay, looks good. Now add these lines to commands.cfg:

# 'check_readynas' command definition
define command{
command_name check_readynas_disk
command_line $USER1$/check_readynas -H $HOSTADDRESS$ -m /usr/local/libexec/nagios/READYNAS-MIB.txt
}

Then add these lines to the server's cfg file for nagios:
define service {
use local-service
host_name my-nas-box
service_description readyNAS RAID
check_command check_readynas_disk
}

Re-start Nagios and watch things start to come good (where "monitored" equals "good).