iostat -x 2 only prints out 0!

[Magicloud Magiclouds <magicloud.magiclouds@gmail.com>]

Hello,
	Recently, I am monitoring a storage for high concurrency IO, to tune it.
	While I am using iostat to see the speed per second, and await value. I 
found out that sometime, when the machine is working, iostat just gives 
out all 0 values for a few times, then return normal, or never until I 
reboot.
	Any idea what is this about?

Thanks.