Direct Attach Storage (DAS) attaches directly to a computer system. The legacy of this term refers generally to hard disk drive arrays attached directly to a server to add capacity for online user files. The interface of choice for these devices was SCSI and they were reserved for database type uses where the speedy input and output (I/Ops) of data was a key to user friendly implementations. The spectrum of hardware and uses has increased, and the deployment of storage strategies has blended to the point that this term now encompasses a much larger variety of products.

Data back-up and disaster recovery devices are some of the most ancient and important of these products. Tape back up has dominated this function and with the advent of automation to remove the greatest cause of failed back-ups, human error, tape remains vibrant and viable, if not the only solution. Direct to disk solutions are thriving and some direct to disk to tape solutions offer the best of features of both deployment strategies. SCSI has again been the interface of choice for these products, at least among businesses with mission critical data requirements, but again DAS is not just for large enterprises. It is also for the single user that does not want to face the inevitability of data loss unarmed.

As it was in the beginning, increased capacity for online data remains an important use of DAS. Many who follow storage cannot help but shake their head at the amazing capacities and myriad interfaces that are offered at affordable prices. These products blur the line between consumer and commercial uses as well as Direct and networked storage. ATA or SATA hard disk drives may be accessed via a SCSI interface for intermediate uses such as streaming video or gaming. Data intensive and mission critical applications may make use of SCSI hard disk drives over a SCSI or Fibre Channel interface to maximize their ease of use.