When you connect an EMC CLARiiON CX series as an external storage system, you must enable SOM 725 on the local storage system. If SOM 725 is not enabled, the external storage system might be blocked when performing maintenance tasks such as rebooting the controller of the external storage system before the firmware update.
If the status becomes Not Ready (that is, the external storage system cannot be accessed), mapped external volumes might be blocked. When restoring a mapped external volume that is blocked, you can select either manual or automatic restore. However, if SOM 1021 is enabled on the local storage system, mapped external volumes that are blocked are restored automatically.
When you attempt to restore a blocked external volume to normal status, if the external storage system has a problem (for example, a failure), the mapped external volume might change immediately back to blocked status because automatic restoration is not possible.
For more information about using SOM 725 and SOM 1021, log on to the Hitachi Vantara Support Connect: https://knowledge.hitachivantara.com/Documents