Industry Concepts:
Storage Area Network (SAN):
A separate computer network, typically based on a ‘fabric’ of fibre channel, switches and hubs that connects storage devices to a heterogeneous set of servers on a many-to-many basis. A SAN can also enable direct storage-to-storage interconnectivity, and lends itself exploiting new breeds of clustering technology and to get the best out of Network Attached Storage devices that can intelligently provide disk and tape capabilities to one or more servers.
The technologies that constitute a SAN are as follows. The critical enabler is fiber technology. This is the ability to send data across fibre optic channels at very high speeds and bandwidths to sites as far away as 10 kilometers. Fiber enabled servers, disk arrays and other intelligent storage and other devices are then connected to the ‘fabric’ by fiber through sophisticated switches and hubs. These may be configured in highly scalable manner to provide access from hundreds of servers in many locations to hundreds of terabytes of shared storage resources attached directly to the Storage Area Network. Zoning and other security facilities are emerging to enable the same levels of security that we have come to demand on the mainframe.
What these technologies do is enable the removal of storage devices from their servers and make the storage generally available across the network on a ‘many to many’ basis, whereby storage is accessed centrally. We are simply moving the storage away from the servers onto its own network allowing storage to be shared among multiple ‘host’ servers without impacting system performance or the primary network.
In brief, SAN simply provides server to storage access across fiber or better yet; SAN enables a disk or tape array to be accessed by two or more servers at high speed across the fibre channel. The benefits include, improved performance, greater connectivity, and the elimination of redundant data enabling long term growth and manageability. A Storage Area Network also expedites the use of advanced clustering solutions thereby enabling new levels of availability and business continuity. A SAN also enables us to relocate backup, restore, file migration and replication of data from the servers and local/wide-area networks and have direct data movement from disks/tapes to other disks/tapes across the SAN fibre.
In order to enable business to operate with a wide-open shared data concept, requires systems to have high performance access to data for all authorized users across the business. According to some, the most useful capability is automatic controlled replication of critical corporate data to where it is needed in business terms. Others might argue that the most appealing benefit of a SAN is that the information is always available. A SAN provides inherently very high availability by the use of automatic data redundancy, automatic backups and the maintenance of nearby disaster recovery copies.
The three primary components of a Storage Area Network:
1. Interface: The Interface is what allows storage to be external from the server and allow server clustering. SCSI, Fibre Channel, and other protocols are common SAN interfaces.
2. Interconnect: The Interconnect is the mechanism these multiple devices exchange data. Devices such as multiplexes, hubs, routes, gateways, switchers and directors are used to link various interfaces to SNA fabrics.
3. Fabric: The platform (the combination of network protocol and network topology) based on switched SCSI, switched Fibre, etc. The use of gateways allows the SAN to be extended across WANs.
Network Attached Storage (NAS):
A disk array that connects directly to the messaging network via a LAN interface such as Ethernet using common communications protocols. It functions as a server in a client/server relationship, has a processor, an OS or mico-kernel, and processes file I/O protocols such as SMB & NFS.
SAN Attached Storage (SAS):
A shared storage repository attached to multiple host servers via a storage interface such as SCSI, FC-AL, or Escon. The SAN is an extended shared storage bus which can be interconnected using similar technologies as LANs or WANs, routers, switches, and gateways.