Direct Attached Storage (DAS) refers to a digital storage system directly attached to a server or workstation, without a storage network in between. It is mainly used as a term to differentiate non-networked storage from SAN and NAS. In information technology, a server is a computer system that provides services to other computing systems—called clients—over a network. ... A computer workstation, often colloquially referred to as workstation, is a high-end general-purpose microcomputer designed to be used by one person at a time and which offers higher performance than normally found in a personal computer, especially with respect to graphics, processing power and the ability to carry... A computer network is a system for communication between computers. ... San or SAN can refer to any of the following: Look up San in Wiktionary, the free dictionary Look up san in Wiktionary, the free dictionary. ... This article or section seems not to be written in the formal tone expected of an encyclopedia entry. ...

Naming

The term did not exist before the advent of networked enterprise storage, though it is often confused with the mainframe term, DASD, which refers to any random-access disk storage system. Another common misconception is that DAS is synonymous with JBOD, a term that refers to storage which is not protected with RAID but actually has no connectivity implications. Enterprise storage is the field of information technology focused on the storage, protection, and retrieval of data in large-scale environments. ... Mainframes (often colloquially referred to as big iron) are large and expensive computers used mainly by government institutions and large companies for legacy applications, typically bulk data processing (such as censuses, industry/consumer statistics, ERP, and bank transaction processing). ... A direct access storage device, or DASD (IPA ) is a form of magnetic disk storage, historically used in the mainframe and minicomputer (mid-range) environments. ... In computer science, random access is the ability to access a random element of a group in equal time. ... Disk storage is a group of data storage mechanisms for computers; data are transferred to planar surfaces or disks for temporary or permanent storage. ... In computing, a redundant array of independent disks (more commonly known as a RAID) is a system of using multiple hard drives for sharing or replicating data among the drives. ... In computing, a redundant array of inexpensive disks, also later known as redundant array of independent disks (commonly abbreviated RAID) is a system which uses multiple hard drives to share or replicate data among the drives. ...

Features

The main protocols used in DAS are SCSI and Fibre Channel. Traditionally, DAS systems enable storage capacity extension for servers, while keeping high data bandwidth and access rate. Most common DAS Systems are made of one or more enclosures holding storages devices such as hard disks, and one or more controllers. Interfacing with the server or the workstation is made through the HBA (Host Bus Adapter). SCSI stands for Small Computer System Interface, and is a standard interface and command set for transferring data between devices on both internal and external computer buses. ... Fibre Channel is a gigabit speed network technology primarily used for Storage Networking. ... Bandwidth is a measure of frequency range, measured in hertz, of a function of a frequency variable. ... Typical hard drives of the mid-1990s. ... In computer hardware, a host adapter or host bus adapter (HBA) connects a host system (the computer) to other network and storage devices. ...

DAS systems typically offer fault tolerance at every level with controller redundancy, cooling redundancy and storage fault tolerance patterns known as RAID. Entry level DAS systems most often are made of an enclosure without active components such as controllers, thus access logic and fault tolerance patterns are provided by the server HBA. In computing, RAID (a redundant array of inexpensive disks, also later known as resilient array of independent disks) is a system which uses multiple hard drives to share or replicate data among the drives. ...

Middle and top range DAS systems provide embedded controllers. RAID management is off-loaded, and simple non-RAID HBAs can be used, lowering costs. DAS controllers also enable shared storage access, which permits multiple servers (usually no more than 4) to acccess the same logical storage unit, a feature that is mainly used for clustering. At this point, top range DAS systems share similarities with entry level SAN systems. Clustering can refer to Computer clustering - (in Computer science) the connection of many low-cost computers using special hardware and software such that they can be used as one larger computer. ...

Disadvantages

DAS has been referred to as "Islands of Information". Disadvantages of DAS include inability to share data or unused resources with other servers. Network-attached storage (NAS) attempts to address this issue, but introduces some new issues as well, such as cost of storage area networks, manageability, security, and contention for resources. This article or section seems not to be written in the formal tone expected of an encyclopedia entry. ...