STORAGE AREA network

as STORAGE AREA network (short SAN, dt. ) One designates memory network within the range of the data processing a network to the binding of non removable disk subsystems and Tape LIBRARies at servers - systems.

Table of contents

definition of a SAN

a STORAGE AREA network (SAN) differs from to local AREA a network (LAN), by representing a network between servers and of the servers used memory resources. The data traffic in a SAN exists mainly inthe transmission of block-based data. Block-based data accesses are used in communication between computers and their non removable disks ( ATA and SCSI). With a block-based data exchange by the computer individual data blocks of a non removable disk are requested (“block 6001 of non removable disk 4”). In contrast becomewith a file-based data exchange over CIFS or NFS whole files requested (“file /home/schmitt/readme.txt”). In most SANs the SCSI becomes - communication protocol used, this touches down then on has a temperature to Channel (fiber plastic) and iSCSI as transportation minutes.

A SAN is an extension of Direct Attached STORAGE ().While a point-to-point connection between a server and a data memory forms, a SAN makes the binding possible of several servers to several memory systems over a network.

development and operational principle

the SAN were developed, over the administrative problem of dedicated non removable disks in servers - systems and/or. Network Attached STORAGE - to work against systems, since with those systems an efficient and flexible use of the storage capacity is only reduced possible.

A further problem of the network attach OD STORAGE systems is that these load additionally the existing net with the accesses to the data media. Further is the Ethernet, over that the network attach OD STORAGE systems with the servers and/or. the Clients connected are not appropriate, with its relatively small framework sizes and relatively large Protokolloverhead for the fast access for mass storages.

SANs are mostly formed today over optical waveguide cable, which becomes thereby assigned system as Have a temperature to Channel designation. A simple STORAGE AREA network consists of a have a temperature Channel SWITCH, one or more non removable disk subsystems and the servers, which over host so mentioned bus adapter, briefly HBA, with which have a temperature Channel SWITCHes are connected.

They work today with ranges within the range of 1 GBit/s to4 GBit/s. Since they use special minutes adapted to the requirement of mass storage use, data transmission rates of theoretically 400 MB/s are possible. In addition comes the concept of the Multi Pathing, which is consistently pursued in the SAN.

Schematic representation of a SANs:

Image:Schema SAN german.png

This example SAN consists those of two Switchen,in each case form an own factory. The servers are tied up, likewise with in each case a HBA to each factory disk the array.

Virtualisierung

a large advantage, which the SAN brings, is the Virtualisierung of the existing disk subsystems. Distributes existing mass storage can virtually like oneonly non removable disk to be treated. The individual server - on this virtual non removable disk partitions are then assigned to systems, which can merge these servers over the host bus adapter like their own non removable disk. The existing storage location can be so many more effectively used and administered, there it at any time inis possible for current enterprise to change the size of the assigned storage area for the servers in the STORAGE AREA network.

A further form of the Virtualisierung brings InfiniBand with itself. Here the PCI bus is replaced by a net and made possible thus that itself network adapters of a server in othersAreas or even buildings to find can.

disaster tolerance

a further large advantage of SANs is their disaster tolerance. So all important elements can be several times redundantly present. In a typical small STORAGE AREA network would be conceivable it that itself at two lying apart as far as possiblePlaces on the working area an identically constructed disk subsystem, each of these disk subsystems in each case finds is connected with one of two also again separately installed Switches. The servers, even if it concerns not distributed systems, have at least two host bus adapter. Of thateveryone is connected to both host bus adapters of a computer with one of the two Switches.

In the upper example now a loss of individual lines, a Switches or even a disk subsystem without impairment of the overall system line would be conceivable.

In larger systems also the servers - systems are redundantly reproached, and frequently to finditself the redundant components on another area or in another city. For the permanent alignment of the data on the disk subsystems dedicated lines are then used within the range of 1 GBit/s to 2 GBit/s. Basis for a SAN cross-linking in the WAN - usually glass fiber TZE form range,those often, in order to be attained a better utilization of fiber, be wired with WDM - systems, which appropriate minutes as have a temperature to Channel or can transport Gigabit Ethernet Frames over very far distances. To consider here however the latency is, those with transmissions over larger distances onelarge role plays.

also

today, after the SAN within many ranges was established, a complete compatibility between the components of all manufacturers is not still given problems. With the employment of new components these must therefore costing and time-consuming on the compatibility with thatexisting components to be examined. Many users committed themselves therefore in their STORAGE AREA networks to the components of a manufacturer, in order to go around these complications. Also there are and solutions certified tested by different system manufacturers from the IT and telecommunications (transmission, Switches), which a Interworking guarantees.

see also

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