Device-level i/o utilization information.
Octet 0: average i/o utilization over the latest sample period (percent)
Octet 1: average i/o utilization over the latest minute (percent)
Octet 2: average i/o utilization over the latest hour (percent)
Octet 3: maximum i/o utilization over the latest hour (percent)
i/o utilization = (total octets input + total octets output) / device capacity.