If external storage was implemented that cannot connect to two servers simultaneously, which storage type was used?

The correct answer is DAS, or Direct Attached Storage. DAS refers to storage devices that are directly connected to a server, such as hard drives or SSDs installed in the server or externally connected via USB or Thunderbolt interfaces. Since the storage is directly attached to one server only, it cannot be accessed simultaneously by multiple servers. This direct connection limits its usability to the server it is connected to, making it distinct from other storage options that allow for multi-server access.

In contrast, NAS (Network Attached Storage) provides file-level storage accessed over a network, enabling multiple servers to connect and share data. VSAN (Virtual Storage Area Network) and SAN (Storage Area Network) offer shared block-level storage that can be accessed by multiple servers simultaneously, unlike DAS. Therefore, the inability of data to connect to two servers at once is a characteristic unique to DAS.