CMMVC9356E The command failed because an array in the parent pool has an expansion ongoing.

Explanation
This error can occur when an attempt is made to expand an array when there is already an array in
the parent pool that is being expanded. Only one array per parent pool can be expanded at a
time.

User response
Wait for the current expansion process to complete, and then retry the command. You can monitor
the expansion process by using the lsarrayexpansionprogress command.