Last update : September 11, 2013

A Direct-attached storage (DAS) is a file-level computer data storage system directly attached to a server or workstation, without a storage network in between. The main protocols used for DAS connections are ATA, SATA, eSATA, SCSI, SAS, and Fibre Channel.

A storage area network (SAN) is a dedicated network that provides access to consolidated, block level data storage. A SAN does not provide file abstraction, only block-level operations.

A Redundant array of independent disks (RAID) is a storage technology that combines multiple disk drive components into a logical unit. Data is distributed across the drives in one of several ways called RAID levels, depending on what level of redundancy and what performance is required. In RAID 1, data is written identically to two drives, thereby producing a mirrored set.

A Network-attached storage (NAS) is a file-level computer data storage system connected to a computer network, providing data access to a heterogeneous group of clients. A NAS, in contrast to a SAN, uses file-based network sharing protocols such as NFS, SMB, CIFS or AFP. NAS systems are networked appliances which contain one or more hard drives, often arranged into logical, redundant storage containers or RAID arrays. The benefits of network-attached storage, compared to file servers, include faster data access, easier administration, and simple configuration.

The storage space can be comprised of USB or hard disk drives. A NAS can be sold with the drives included or without them. Like PCs, NAS units have memory and processors. With better processors and increased memory, you get better performance from a NAS, just as with PCs. Lunix is usually used as embedded operating system. Noise and security are two other important concerns.

In the last years, NAS devices have been gaining popularity in the home office (SOHO), because they are useful for more than just general centralized storage provided to client computers in environments with large amounts of data. Typical other usages are :

  • load balancing
  • email server
  • web server
  • media server
  • multimedia streaming
  • cloud-based backup
  • low-cost video surveillance
  • BitTorrent client

A list of NAS manufacturers is provided at Wikipedia. A list of links to additional informations about SAN’s is provided below :