While monitoring a http/php server, I needed to do some statistics about php-cgi memory usage.
Playing with memory_limit in PHP, we wanted to know the average memory usage per php-cgi process. This is easily calculated with our best friend awk.
First, get the number of php running processes:
# ps aux | grep php-cgi | grep -v grep [...]

While reading this interresting article on benchmarking disks, Benjamin Schweizer pointed out a link to a python tool he wrote: benchmark disks IOs.
I made a try on different available servers.
Server 1

PowerEdge 2950 – Intel(R) Xeon(R) CPU 5160  @ 3.00GHz
Dell PowerEdge Expandable RAID controller 5 (LSI Logic SAS based MegaRAID driver, PERC 5/i Integrated)
6 disks RAID [...]