The binary "iostat" comes from the package "sysstat" and is available on all Linux/Unix like platforms.
Use the "-m" option to give you what you probably want, which is to see in MB/s how much bandwidth each disk is doing.
iostat -m
Linux 2.6.24.2 ((none)) 04/16/10
avg-cpu: %user %nice %system %iowait %steal %idle
........