The question states "data on the SAN", so if you encrypt data at rest, this will prevent data compromised.

An intermediate distribution frame (IDF) is a free-standing or wall-mounted rack for managing and interconnecting a telecommunications cable between end-user devices and the main distribution frame (MDF).
DNS has nothing to do with LAN network connectivity. OS version and Switch vendor is not a thing. And the HIDS is detection not prevention. The only choice left is VLAN.

RAID 6 provides excellent redundancy by using dual parity, which allows for the failure of up to two drives without data loss. With eight drives in RAID 6, the usable capacity is calculated as N-
2N - 2N-2 (where NNN is the total number of drives). Thus, with eight drives, the usable storage would be six drives' worth of capacity. This provides a good balance between redundancy and usable storage.

When you research server clustering, you frequently hear the terms failover and failback. Failover refers to the failure of the active service provider node and passive node's taking over of its responsibilities. At that point, the server that was the passive node becomes the active node. It services clients and handles the cluster's duties. Once the original active node returns to service, you may set it to act as the new passive node, or you may shift the services back to it, causing it to take back its active node role and relegating the formerly passive server to its original role. The term failback refers to the service returning to the original active node.