Direct-attached storage (DAS) is computer storage that is connected to one computer and not accessible to other computers. For an individual computer user, the hard drive is the usual form of direct-attached storage.
In the enterprise, individual disk drives in a server are called direct-attached storage, as are groups of drives that are external to a server but are directly attached through SCSI, SATA and SAS interfaces. DAS can provide end users with better performance than networked storage can because the server does not have to traverse the network in order to read and write data. That is why enterprise organizations often turn to DAS for certain types of applications that require high performance. Microsoft, for example, recommends that Exchange installations use DAS.
In the past, direct-attached storage was often criticized as an inefficient way to manage enterprise storage because DAS storage can't be shared and it does not facilitate failover should the server crash. As virtualization has become mainstream, however, the advantages that DAS offers are once again gaining popularity.