In a Non-Disruptive Upgrade (NDU), ensuring that the host is correctly multipathed and balancing I/O across all paths is critical before taking a controller down. If a host is only using paths to the controller about to be rebooted (CT0, for example), taking that controller offline would cause an outage.
The command iobalance --sampletime 30 (or its wrapper purehost monitor --balance) is the standard tool used during the upgrade procedure to validate this state.
* iobalance : This script samples the I/O throughput on all ports for a specified duration (e.g., 30 seconds).
* It analyzes the distribution of I/O. If it detects that I/O is heavily skewed or missing entirely on the
"secondary" paths (the ones that will survive the reboot), it flags a warning.
* This allows the Implementation Engineer to pause and remediate the host multipathing configuration (e.
g., fixing a bad cable or zoning issue) before proceeding with the controller removal, ensuring the NDU remains truly non-disruptive.