Direct-attached storage (DAS) is digital storage directly attached to the

computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as C ...

accessing it, as opposed to storage accessed over a computer network (i.e. network-attached storage). DAS consists of one or more storage units such as

hard drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magnet ...

solid-state drive A solid-state drive (SSD) is a solid-state storage device that uses integrated circuit assemblies to store data persistently, typically using flash memory, and functioning as secondary storage in the hierarchy of computer storage. It is ...

optical disc drive In computing, an optical disc drive is a disc drive that uses laser light or electromagnetic waves within or near the visible light spectrum as part of the process of reading or writing data to or from optical discs. Some drives can only r ...

s within an external enclosure. The term "DAS" is a retronym to contrast with storage area network (SAN) and network-attached storage (NAS).

Features

A typical DAS system is made of a

data storage device Data storage is the recording (storing) of information (data) in a storage medium. Handwriting, phonographic recording, magnetic tape, and optical discs are all examples of storage media. Biological molecules such as RNA and DNA are conside ...

(for example

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s holding a number of

hard disk drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magnet ...

s) connected directly to a computer through a host bus adapter (HBA). Between those two points there is no network device (like hub, switch, or router), and this is the main characteristic of DAS. The main

protocol Protocol may refer to: Sociology and politics * Protocol (politics), a formal agreement between nation states * Protocol (diplomacy), the etiquette of diplomacy and affairs of state * Etiquette, a code of personal behavior Science and technology ...

s used for DAS connections are ATA, SATA, eSATA, NVMe,

SCSI Small Computer System Interface (SCSI, ) is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, electrical, optical and logical interface ...

SAS SAS or Sas may refer to: Arts, entertainment, and media * ''SAS'' (novel series), a French book series by Gérard de Villiers * ''Shimmer and Shine'', an American animated children's television series * Southern All Stars, a Japanese rock ba ...

USB Universal Serial Bus (USB) is an industry standard that establishes specifications for cables, connectors and protocols for connection, communication and power supply (interfacing) between computers, peripherals and other computers. A broad v ...

, USB 3.0 and IEEE 1394.

Storage features of SAN, DAS, and NAS

Most functions found in modern storage do not depend on whether the storage is attached directly to servers (DAS), or via a network (SAN and NAS). In enterprise environments, direct-attached storage systems can utilize storage devices that have higher endurance in terms of data workload capability, along with scalability in the amount of capacity that storage arrays can achieve compared to NAS and other consumer-graded storage devices.

Advantages and disadvantages

The key difference between DAS and NAS is that DAS storage does not incorporate any network hardware and related operating environment to provide a facility to share storage resources independently of the host so is only available via the host to which the DAS is attached. DAS is typically considered faster than NAS due to lower latency in the type of host connection although contemporary network and direct connection throughput typically exceeds the raw read/write performance of the storage units themselves. A SAN (storage area network) 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.

References

Englander, I. (2014). The architecture of computer hardware, systems software, & networking: An information technology approach (5th ed.). Retrieved from https://online.vitalsource{{Dead link, date=November 2019 , bot=InternetArchiveBot , fix-attempted=yes . com/#/books/9781118803127 Computer data storage

Features

Storage features of SAN, DAS, and NAS

Advantages and disadvantages

See also

References