Explanation/Reference:
The keystore is tied to the storage processors, so care must be taken when performing service operations in order to preserve the encryption keys. In the event that the chassis and both storage processors need to be replaced, both storage processors should not be replaced at the same time. Instead, the chassis replacement should be followed while retaining one SP until the array is back online before replacing the second SP. In the case that storage processors have already been replaced at the same time and the keystore was lost, the keystore may be restored from an external backup.

Explanation/Reference: https://www.dellemc.com/resources/en-us/asset/white-papers/products/storage/h15088- dell_emc_unity-replication_technologies.pdf (7)

Explanation/Reference:
UnitVSA features Host I/O limits, also known as Quality of service.
The EMC [Physical] Unity array comes with a pack of new hardware and software features focusing on the true unification:
Support for setting up Host I/O limits, also known as QOS, providing a more predictable performance

for the workloads by putting limits on I/O throughputs and bandwidth
DPE reduced from a 7U footprint to an innovative 2U footprint

12 GB SAS back-end for the Unity DAEs; EMC VNX/VNXe supported only 6 GB SAS backend

Completely redesigned user interface based on HTML5

References: https://www.emc.com/collateral/white-papers/h15092-emc-unity-unity-vsa.pdf (page 16)
http://www.presidio.com/blog/technical-summary-emc-unification-unity