Direct Attached Storage (DAS)

DAS is short for direct attached storage.

Direct attached storage (DAS), also called direct attach storage, is digital storage that is attached directly to a computer or a server. In other words, DAS isn’t part of a storage network. The most familiar example of DAS is the internal hard drive in a laptop or desktop PC. In practice, the phrase direct attached storage is used most often in reference to dedicated storage arrays attached directly to servers. It is used to distinguish DAS from networked storage arrangements, like SAN or NAS devices.
DAS Devices Explained

DAS can refer to a single drive or a group of drives that are connected together, as in a RAID array. In addition, DAS devices can be housed inside a PC or server (as is the case with internal hard drives) or outside the PC or server (as is the case with external hard drives and storage appliances). Multiple systems can use the same DAS device, as long as each PC or server has a separate connection to the storage device.

The primary benefits of DAS include simplicity and low cost. Installing networked storage systems, like NAS and SAN devices, requires more planning, as well as the purchase and deployment of network hardware, such as routers and switches, in addition to appropriate cabling and connections. By contrast, most PCs and many servers come with DAS already installed, and if you want to add more direct attached storage, generally all you need to purchase is a storage device and possibly a cable. Maintaining DAS is also very simple; by contrast, SAN and NAS solutions usually require management software and may require monitoring software as well.
The Difference Between DAS, SAN and NAS

In the early days of computing, DAS was the only type of storage available. In fact, the term direct attached storage didn’t come into use until much later when people needed a way to differentiate between traditional storage and SAN and NAS devices.

NAS (network attached storage) offers file-level storage for end users that are connected to a network. The advantage of NAS over DAS is that it simplifies file sharing among multiple users while potentially offering faster performance than a traditional file server.

SAN (storage area network) refers to a network of storage devices that provides block-level storage for servers in a data center. For large organizations with many servers, SAN offers better performance and flexibility than DAS, along with potential cost savings, although SAN hardware can be costly.

Many SAN and NAS devices can also be used as DAS devices. The difference lies in whether they are attached directly to a server or attached to a network via routers and switches.