Best way to measure disk bandwidth usage

[Andrea Venturoli]

Hello.
I've got a couple of servers which I'd like to keep an eye on in order 
to check wether their storage subsection is providing enough throughput 
or wether disk i/o is their bottleneck.

I know how to check this wrt cpu usage, memory size, network throughput, 
but I'm totally lost when it comes to disk i/o.
I can run top and press 'm': this will allow me to know which processes 
are using disk the most, but not wether I'm exploiting the hardware to 
the limit or just to a small fraction of what it can do.

Any hint?

  bye & Thanks
	av.