General disk monitoring question

Hi, 

I have couple general disk monitoring questions. Basically we use iSCSI volumes which I would like to monitor for performance issues.

Our storage has one array with multiply LUNs so in this case I guess the best way to monitor iSCSI volumes is to use Logical Disk counters?

Could you provide me could of counters what could help identify iSCSI volume problems? 

I was thinking about:

"\Logical Disk(*)\Avg. sec/Read” < 15 ms
“\Logical Disk(*)\Avg. sec/Write" < 15 ms

I like these counters as you compare to exact value in this case 15 an configure the triggers. Any other examples?

Also was thinking about I/O counters:

 But these counters depends on amount of data being write and read (Avg. Disk Bytes/Read, Avg. Disk Bytes/Write). As for 8kb per read and for 256kb per read I/O will different. 

So is there any way to configure counters for troubleshooting iSCSI volumes bottlenecks? and howinterpret them? 

thanks