While it is recommended to perform the upgrade process during periods of low to no I/O, as long as the host side is properly setup to failover the paths, there should be no issue with performing the u...While it is recommended to perform the upgrade process during periods of low to no I/O, as long as the host side is properly setup to failover the paths, there should be no issue with performing the upgrade while servicing I/O. As part of the upgrade process, one controller will be placed in an unavailable state and each of the volumes that the controller owns will be moved to the alternate controller while the upgrade is underway.