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All upgrades to add hardware to a PowerMax array are non-disruptive, including:
Additional capacity is added to a system either by adding drives to available drive slots in existing DAEs or as part of adding an engine to a system.
No user action is required for the system to begin using the new capacity. New writes are distributed across the system with some bias towards drives which have the most available capacity, which in this case will be the new drives. Background rebalance activities take place to spread the TDATs on the newly added drives and existing data across the compression pools.
PowerMaxOS will bring each compression pool into a reasonable balance transparently to the host applications. Servicing host I/O takes priority over the background activities. Therefore, the total time to achieve a balance will depend on overall system activity and total system capacity, used capacity, and amount of newly added capacity.