It is easy to understand that with that number and the fear of what happens when the system breaks down they decided to go for a fully redundant solution.
Moreover since also their playout machines play out directly from the storage with limited buffering, it should also be a failover system with a short failover time and transparent to all connected.

Another important factor is the ability that maintenance such as checks and updates can be done while the DDP is in full operation.

The HA DDP consisted of the Dual HA DDPHead, a DS1024, 2U with 16 x 3.82 TB SAS SSDs defined as Cache plus a 16 bay filled with 20TB drives, so 360TB configured as raid 6.
The Cache size of 51TB usable capacity after raid 5 is sufficient to work from and to the cache while removing finalized project from the cache and ingesting projects material to the cache.
Because of this cache based workflow the bandwidth of 2GB/s is always enough no matter which video/audio format is used.

There are occasions where data from finalized projects need to be accessed again.
In those cases the material comes from the hard disks.
Cache and hard disks can be accessed simultaneously.
On top the system runs our Audio/Video File System – A/V FS – as file system.
A/V FS is a high availability scale out file system specially developed for M & E.
The project / file based caching mechanism is a unique property of A/V FS.