DAS is Direct-Attached Storage. A typical DAS system is made up of a storage device — typically a hard disk drive (HDD) or solid state drive (SSD) — attached directly to the computer accessing it, and dedicated to that computer.  DAS is connected directly via:

• an onboard or external connection; or
• a host bus adapter (HBA) with either an internal or external cable

Between the two end devices, there is no network device (such as a hub, switch, or router), and this is the main characteristic of DAS. The main protocols used for DAS connections are SAS, SATA, NVMe, USB, and IEEE 1394.

DAS differs from storage accessed over a network, called a network-attached storage (NAS). Likewise, DAS is simpler than a SAN (storage area network), a network of storage devices accessed by multiple servers or computers, which view the storage devices as though they are locally attached.

Aside from how storage is shared, and the protocols used to transmit data, the main differences between DAS, NAS and SAN are cost and scalability. Another key difference is they utilize different storage structures: DAS uses local block storage, NAS uses shared files, and SAN uses networked block storage.

Where and When Do You Use DAS?

A DAS system is practical and cost-effective if you don’t have the need or resources for networked storage solutions. DAS is perfect for businesses and organizations that share data locally, rather than across their network. DAS can be configured on individual servers with storage internal to the server or in external enclosures. Maintenance and support are minimized given this simple structure.