IBM Midrange System DS4000 Series Hardware Manual page 358

You must perform the upgrade offline.
For most failover drivers to take effect, you must reboot the host.
Caution: Before using the IBM System Storage DS4000/DS5000 Controller Firmware
Upgrade Tool, it is important that all data be completely backed up and that existing system
configurations be saved. Once the tool has completed an upgrade, controllers cannot be
returned to previous firmware version levels.
There is a potential loss of data access, so make sure the firmware you download is
compatible with the Storage Manager software that is installed on your storage subsystem.
If non-compatible firmware is downloaded, you might lose access to the drives in the
storage subsystem, so upgrade Storage Manager first.
The Firmware Upgrade Tool will also automatically perform its own diagnostic check on these
systems to determine if they are healthy enough to perform a controller firmware upgrade.
These are possible status conditions after the health check:
Optimal: Every component in the device list is in the desired working condition.
Needs Attention: A problem exists with the device that requires intervention to correct it.
Fixing: A Needs Attention condition has been corrected, and the device is currently
changing to an Optimal status.
Unresponsive: The storage management station cannot communicate with the device, or
one controller, or both controllers in the storage subsystem.
Contacting Device: The management software is establishing contact with the device.
Needs Upgrade: The storage subsystem is running a level of firmware that is no longer
supported by the storage management software.
Refreshing: The status is currently refreshing. This is a transition state.
Not Upgradable: This subsystem does not fit the requirements to upgrade the firmware.
Either it is already upgraded or it is not a DS4200, DS4700, or DS4800 storage
subsystem.
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IBM Midrange System Storage Hardware Guide