For Nagios monitoring, I assume you're trying to alert on storage latency. If so, I'd recommend not trying to interpret information about latencies seen on the disks behind the Nimble because this disk latency will not directly correlate with the iSCSI latencies observed by the host.
For best results, I'd recommend monitoring the storage latency from the host side. This way, you are also sure to trigger an alert if connectivity issues or network congestion are impacting services. Scripting on iostat may be one way to monitor storage latency to a Nimble iSCSI-mounted LUN, from a Linux host, as an example.
Thanks for your answer.
I am already monitoring the "client" side of the iscsi mounts in linux, but there are 3 osses connected here, Linux, Novell (partially Linux) and Windows.
I have no idea (yet) on how to do this for windows.
hmm, well, back to the ol' drawing board it is then.