San Implementation

SAN implementation over Gigabit Ethernet
A Storage Area Network is virtualized storage.


A storage area network (SAN) is a dedicated, centrally managed, secure information infrastructure, which enables any-to-any interconnection of servers and storage systems.
A SAN can be configured to provide a nearly infinite pool of storage that you can grow and move between servers as they need it. The storage can be added to and removed without requiring the server to be rebooted. The services provided by the server continue to operate without interruption.

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The primary purpose for implementing a SAN is to provide a large storage pool that multiple hosts could access. Common storage configurations involve direct attachment of storage to a host. This storage is only available for use by that host. If there were another host that needed storage, you would need to buy additional storage to install on that host.The host with excess capacity would not be able to share its storage with another host.

In a SAN, all networked devices share storage capacity as peer resources; they are not the exclusive property of any one server. You can use a SAN to connect servers to storage, Servers to each other, and storage to storage through hubs or switches. A SAN carries only I/O traffic between servers and doesnt carry any general-purpose traffic such as e-mail. Storage area networks remove data traffic, like backup processes, from the production network giving IT managers a strategic way to improve system performance and application availability.

As SAN technology develops, it is growing beyond the use of any one kind of technology. A SAN can be configured to use a number of protocols such as IP or Fibre Channel over a network medium like Ethernet or ATM. FC over Ethernet supports up to 1.06 Mbps. Emerging standards that are still being defined include Gigabyte System Network(GSN) which promises full-duplex 6.4 Mbps over a 40 meter copper cable.

Storage area networks improve data access. Using Fibre Channel connections, SANs provide the high-speed network communications and distance needed by remote workstations and servers to easily access shared data storage pools. IT managers can more easily centralize management of their storage systems and consolidate backups, increasing overall system efficiency. The increased distances provided by Fibre Channel technology make it easier to deploy remote disaster recovery sites. Fibre Channel and switched fabric technology eliminate single points of failure on the network. With a SAN, virtually unlimited expansion is possible with hubs and switches. Nodes can be removed or added with minimal disruption to the network.

What is Gigabit Ethernet.

Gigabit Ethernet supports 1000 Mbps over Ethernet media. Because it is similar to existing Ethernet and Fast Ethernet standards in that it uses the same frame format and collision detection mechanisms, Gigabit Ethernet is easy to integrate with existing Ethernet networks. It was designed as a Ethernet backbone switch-to-switch and switch-to-server technology.

To provide the speed increase from 100 Mbps Fast Ethernet up to 1 Gbps, several changes needed to be made to the physical interface of Gigabit Ethernet versus Fast Ethernet. It was decided that Gigabit Ethernet will look identical to FibreChannel at the physical layer. By taking advantage of the existing high-speed physical interface technology of FibreChannel while maintaining the IEEE 802.3 Ethernet frame format, backward compatibility for installed media, and use of full or half-duplex carrier sense multiple access collision detect (CSMA/CD), customers will be able to use their existing knowledge base to manage and maintain gigabit networks. They would not have to throw away their existing network infrastructure.
Gigabit Ethernet is intended for Fast Ethernet backbones and switch to server links where existing Ethernet networks are being aggregated onto the faster Gigabit Ethernet speeds. A company planning a gigabit network would purchase switches supporting Gigabit Ethernet and plug the existing Fast Ethernet switches and hubs into them. Thus cascading the higher bandwidth speeds down from the wiring closet and data center to the servers and end users PCs.

How does Gigabit Ethernet fit in the SAN picture
Gigabit Ethernet is just one way of passing Fibre Channel storage to a server. You would combine multiple server connections over Gigabit Ethernet through a switch. NAS is something that could easily be attached through a Gigabit Ethernet network. At some location on the lan, clients would be aggregated into a Gigabit Ethernet backbone and then to the NAS.

You wouldnt directly connect a host to a pool of storage through a Gigabit Ethernet connection. Since the disks and the storage processors for the time being are either SCSI or SSA or Fibre Channel based, the physical interconnect will be Fibre or SCSI or SSA.
If you connect servers via Gigabit Ethernet to a storage pool, you would need switches that can translate disk I/O to a protocol that can be sent over Ethernet. A method of moving disk I/O commands over an Ethernet lan is called GSN or a Gigabyte System Network switch. A GSN switch can accept any number of Ethernet or faster connections and consolidate them to provide up to a 800 MB per second connection to a storage resource. A GSN can accept connections from eight standard Fibre Channel storage subsystems to equal the bandwidth on one GSN port.

The switch is crucial to the interoperability of the different SAN entities. The switch is responsible for the conversion or the translation of disk I/O commands into a form that can be sent over the network medium. The network can be Fibre Channel, Fast or Gigabit Ethernet, ATM, FDDI, GSN (Gigabyte System Interconnect), or HIPPI (High Performance Parallel Interface).

One benefit is that you wouldnt need to purchase anything more expensive than an Ethernet card to connect a host to the SAN. The SAN would still be FC but the switch would allow different types of connections to be made to the storage resource without buying Fibre Channel adaptors for each host you wanted to attach to the storage. You can even aggregate multiple end user computers over a Ethernet connection through a GSN switch and give SAN access to any PC on the network. Another benefit is that you can continue to use your existing FC-AL or SAN fabric. The switch would sit between the storage pool and all of your different hosts and handle the conversion and routing of data between the servers and their virtual disks.


The phrase SAN implementation over Gigabit Ethernet is a misnomer. You are using FC or SCSI disks at all times. The SAN is implemented using the common Fibre Channel or SCSI technology. The hosts however would use a variety of methods to attach to the storage pool. The usual connection methods try to avoid introducing bottlenecks between the server and the storage pool. If you combine the different links from the servers together over a 1000Base switch, you would make better use of the available bandwidth to the storage.

Using Gigabit Ethernet in this way makes for an excellent low-cost connection to storage resources. Since many customers already have a Ethernet network in place the additional cost of the GSN capable switch is the only additional cost. Once the switch is attached to the SAN, the benefits of a SAN solution can be pushed out to more client computers in the company.


Bibliography
http://www.zdnet.com/eweek/reviews/1201/01gig.html#Reference
http://www.iol.unh.edu/consortiums/ge/index.html
http://www.cisco.com/warp/public/729/gigabit/index.shtml