Some great advice from Dan Morgan at Forsythe
Oracle ODA Maintenance Alert:
Oracle ODAs perform extensive diagnostics immediately following an appliance reboot. Be sure that you do one before you begin a patching exercise. Our standard patching procedure is to always perform a reboot before patching and doing so saved our customer’s data last week as we had an incident where following a reboot the ODA went into an ASM rebalancing with Power = 1 that could not be altered as the result of a physical drive that had unrecoverable read errors.
Had the patching taken place without the reboot the drive failure would likely not have been discovered until too late to guarantee no data loss.