Direct Attached Storage

Direct Attached Storage (DAS) or server -attached storage refers to a single host attached hard drives that are located in a separate housing.

The usual interfaces are SCSI and SAS increasingly. However, are all possible block-oriented transmission protocols for direct ( point to point ) connections, for example, ATA / ATAPI, FireWire, eSATA and USB. In contrast, there are Fibre Channel, iSCSI, or FICON / ESCON that belong to the network-oriented SAN concepts. The operated as THE media provides the same performance as directly installed in the host drives; tailed in the SAN disk recorded by the network-oriented approach, however, usually slight performance hit.

In contrast to Network Direct Attached Storage, Network Attached Storage or Storage Area Network other computers the DAS disks can usually use only via network and the host to which they are physically connected. However, an exception in the field of high-availability form "Shared SCSI " installations where two hosts together have access to a SCSI bus, for example, by a suitable cluster file system (eg, GFS ) can share access to the drives.

Another increasingly important expectant use of Direct Attached Storage (DAS) is an extension of Network Attached Storage (NAS) and Storage Area Network ( SAN) disk arrays. This is made possible by faster and faster ( point to point ) compounds such as SATA 3 and PCI Express. It operates the NAS or SAN hosts, and must offer the corresponding host -capable extension interfaces (eg USB 3.0 or eSATA).

Benefits

  • Low hardware overhead.
  • Conceptually quickly, the real speed is of course dependent on the technique used.
  • No additional protocol stack. The point-to - point connection is forwarded directly to the device / disk.

For example, eSATA, only the plugs / sockets mechanically Different from SATA, the data flow can immediately 1:1 therefore be sent directly to the hard drives.

Disadvantages

  • Only exclusively bound to a host

Disadvantages occur in DAS systems when multiple systems are used at different servers. All of these devices need to be monitored and administrated with extra effort.

  • Sometimes special protocol extensions are required ( eg SATA Port Multiplier )

To set the time many DAS systems to eSATA SATA Port Multiplier a base internal one, but quite popular Intel chipsets ( ICHx ) have this protocol usually not implemented, so you have other SATA controller retrofitted to use this feature.

See also

  • Storage Area Network
  • Network Attached Storage
  • Network Direct Attached Storage
Host (network) IEEE 1394 Global File System
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