System profiling tools?

[Alan Dayley]

Let's suppose that I have a Linux file server.  It is working well and
does nothing (discounting cron or other system processes) but serve
shares.

The server has 1Gb/s ethernet interface to the net and four 150MB/s SATA
hard drives in Linux software RAID 5.  But, for all this hardware
bandwidth I only get an effective throughput from my server of 40MB/s data
transfers.

I want to find the overhead.  Is it the software RAID?  Is it the SATA
controller?  Is it the IP stack?  Or a combination of these or other
things?

What software tools are available to profile my system and help pinpoint
the bottle neck(s)?

Alan