Direct-attached storage


Direct-attached storage is digital storage directly attached to the computer accessing it, as opposed to storage accessed over a computer network. Examples of DAS include hard drives, solid-state drives, optical disc drives, and storage on external drives. The name "DAS" is a retronym to contrast with storage area network and network-attached storage.

Features

A typical DAS system is made of a data storage device connected directly to a computer through a host bus adapter. Between those two points there is no network device, and this is the main characteristic of DAS.
The main protocols used for DAS connections are ATA, SATA, eSATA, NVMe, SCSI, SAS, USB, USB 3.0 and IEEE 1394.

Storage features common to SAN, DAS and NAS

Most functions found in modern storage do not depend on whether the storage is attached directly to servers, or via a network.

Advantages and disadvantages

The key difference between DAS and NAS is that DAS storage is only directly accessible from the host to which the DAS is attached. A DAS does not incorporate any network hardware and related operating environment to provide a facility to share storage resources independently. The storage presented by a DAS to a connected host can of course be shared by that host. A SAN has more in common with a DAS than a NAS with the key difference being that DAS is a 1:1 relationship between storage and host whereas SAN is many to many.