Wandering Thoughts archives

An important difference

As a note to myself, there is an important difference between

; timeio 10G </dev/zero >somefile
; timeio <somefile

and what I actually intended to do for the second command,

; timeio <somefile >/dev/null

Forgetting this difference has several times left me wondering why disk IO read rates on test systems seemed to have dropped by several orders of magnitude from what they should be for no apparent reason. (Since writing null bytes to your screen is a great way to burn CPU and possibly network bandwidth while doing nothing visible at all.)

(Why I have my own command to measure bulk IO performance is a topic for another entry.)