Storage Area Network
As a Storage Area Network ( SAN ) and storage network is known in the field of data processing network for connecting disk subsystems ( disk array ) and tape libraries on server systems. Storage Area Networks are designed for serial, continuous high-speed transmission of large amounts of data. Today are based on high-availability, high-performance installations on the implementation of the Fibre Channel standards in SMEs from cost considerations also apply to IP.
Definition of a SAN
A SAN is an extension of Direct Attached Storage (DAS ), the disk storage capacity is assigned to a server over a network, but also within operational limits / requirements dynamically, ie, at any time, may otherwise be associated with a server. The latter functionality is mainly implemented in SAN -compatible disk arrays. While DAS provides a point-to- point connection between a server and a direct-attached data storage, a SAN allows multiple servers to multiple storage systems to connect over a network, even over long distances.
In a SAN data accesses done as DAS block- based, ie manages the access to the storage device and may be on this befindliches file system through the accessing computer. For NAS, however, accesses via SMB / CIFS or NFS on all files (for example: " / home / user / readme.txt" ) or excerpts from files at a remote location, its file system is managed in this case, especially in server. SANs use a SCSI communication protocol is usually used that is based on Fibre Channel or iSCSI as the transport protocol. Rare and virtually represented only in the SOHO area, implementations are based on AoE. There are also first SAN solutions based on other communication models such as RSIO or Infiniband and in the context of a convergence of IP and storage networking.
Structurally, a SAN is constructed analogously as a Local Area Network ( LAN): So there are hubs, switches and routers.
Development and operating principle
The SAN was designed to counteract the problem of dedicated hard disk management in server systems or network attached storage (NAS) systems, as these systems efficient and flexible use of the storage capacity is limited.
Another problem of the NAS systems is that these additional strain on the existing LAN with access to the data. Furthermore, the Ethernet, through which the NAS systems are connected to the servers and the clients, not designed with its small frame sizes, and thereby its relatively large protocol overhead for fast access to mass storage.
SANs today are mostly made via fiber optic cable; the system employed here is referred to as Fibre Channel. A simple SAN consists of a Fibre Channel switch, one or more disk subsystems and servers that are connected via so-called host bus adapter HBA short, to the Fibre Channel switch.
Today you are working with transfer rates up to 16 Gbit / s Since they use a special, adapted to the requirements of mass memory usage protocol transfer rates theoretically 1.6 GB / s are possible. In addition, the concept of multi-pathing, which is consistently pursued in the SAN.
This example consists of two SAN switches, each constituting a separate fabric. The servers are connected each with a host bus adapter to any fabric, as well as the disk array.
Disaster tolerance
Another great advantage of SANs is their disaster tolerance. This includes disk subsystems that have internal components with integrated RAID functionality and the various RAID levels (usually RAID 1, 10, 5, 50, 6 or 60) control automatically and server- independent. Next all major systems several times ( redundant) can be designed. In a typical small storage area network, it is conceivable that on the premises each an identical disk subsystem is possible at two widely separated locations, each of said disk subsystems connected to a switch of two separately installed again. The server, if it is not also distributed systems, have at least two host bus adapters. By both of the host bus adapters of a computer is connected to each one of the two switches. The data of both disk subsystems, depending on the installation, either by the server or automatically, through an integrated directly into higher disk subsystems functionality, mirrored ( RAID 1).
In the above example a failure of individual wires, a switch, or even a disk subsystem without affecting the overall system performance would now be possible.
In larger fault-tolerant systems and server systems are maintained redundantly. Next, it is useful to protect against disasters such as elemental damage, or terror, to accommodate the redundant components on another, more distant location. For continuous comparison of the data on the disk subsystems then leased lines are usually in the range of 1 Gbit / s to 9 Gbit / s used. Form the basis for a SAN networking in the WAN area usually fiber-optic networks that guarantee the galvanic isolation. The glass fibers are often in order to obtain a better utilization of fiber, connected with Wavelength Division Multiplex (WDM ) systems. By appropriate protocols such as Fibre Channel or Gigabit Ethernet data can be safely transported over very long distances. It should be noted here, however, the latency over long distances plays an important role in transmission.
Problems
Even today, after the SAN has become established in many areas, a full compatibility between the components of all manufacturers is not necessarily guaranteed. When new components, they must therefore be considered costly and time- consuming to the compatibility with the existing components. Many users have therefore in the past been determined in Storage Area Networks on the components of a single manufacturer to avoid these complications. The Storage Networking Industry Association ( SNIA ) is an initiative of various manufacturers who want to avoid such problems by uniform standards. Various manufacturers guarantee but in the meantime the required functionalities in an extensively tested of them multi-vendor configuration.
History
Technologically speaking, is a SAN a development introduced by IBM ESCON technology, respectively. based on them FICON technology.