The redundancy levels refer to the level of guarantee for data access given a single failure among the data storage components. The SUT must implement one of the following Redundancy Levels:
Redundancy Level One (Durable Media Redundancy): Guarantees access to the data on Durable Media when a single Durable Media failure occurs.
Comment: The intent of this redundancy level is to test the ability of the Durable Media environment to survive the failure of a single Durable Medium and continue processing requests from the Operating System and/or DBMS.
Example: The Sponsor has implemented RAID-1 (mirroring) on the disks within an enclosure. The Sponsor must maintain access to the data on the remaining disks despite the induced failure of a single disk.
Redundancy Level Two (Durable Media Controller Redundancy): Includes Redundancy Level One and guarantees access to the data on Durable Media when a single failure occurs in the storage controller used to satisfy the redundancy level or in the communication media between the storage controller and the Durable Media.
Comment: The intent of this redundancy level is to test the ability of the implementation to survive the failure of a storage controller responsible for implementing Redundancy Level One.
Example: If Redundancy Level One is satisfied by implementing RAID-5 protection within a disk enclosure, then Redundancy Level Two would be tested by failing the hardware used to implement the RAID-5 protection.
If the controller implementing the RAID-5 is contained within the disk enclosure (or similar externally attached device), then the Sponsor must demonstrate they can still access the data stored within the enclosure.
If the controller implementing the RAID-5 is separate from the enclosure containing the disks, and the controller is not being used as a Durable Medium (e.g. mirrored write caches), then it is sufficient to fail the communications between the controller and the enclosure.
Redundancy Level Three (Full Redundancy): Includes Redundancy Level Two and guarantees access to the data on Durable Media when a single failure occurs within the Durable Media system, including communications between Tier B and the Durable Media system.
Comment 1: The Durable Media system includes all components necessary to meet the durability requirements defined above. This does not include the Tier B system or the system bus, but does include the adapter on the system bus and any and all components "downstream" from the adapter.
Comment 2: The intent of this clause is to test the ability of the Tier B system to withstand component failures and continue processing of the Transactions.