258 IBM Midrange System Storage Hardware Guide
4.10.10 Automatic firmware synchronization
The Automatic Code Synchronization (ACS) feature ensures that both controllers within a
storage subsystem are executing the same version of the controller firmware. The primary
purpose of this feature is to reconcile the possible difference in controller firmware version
present on a replacement controller. ACS is also used to address inconsistent versions of
firmware that can occur without controller replacement if a firmware upgrade is interrupted.
The replacement of both controllers is not a recommended operation, because ACS is
intended to use the firmware image on the remaining native controller to resolve the
inconsistency. ACS does address the replacement of both controllers. In this case, ACS
synchronizes to the newer of the two firmware.
A failure to successfully transfer the incumbent image from the native to the foreign controller
results in the native controller holding the alternate controller in reset.
The ACS feature behavior is based on three key persistent data representations:
The serial number of each controller.
The serial numbers of the last known native controllers. The identities of the last known
controllers are contained within the metadata on the native drive set.
The firmware version number of the incumbent firmware. This is the firmware associated
with the metadata on the native drive set. The version of the incumbent firmware is stored
within the drive metadata.
The controller firmware uses this information to determine what ACS action is required. If the
serial number of a controller does not match the serial number for the slot in which it resides,
this controller is considered to be
foreign for the purposes of ACS, and a firmware
synchronization occurs.
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