1. Introduction to Networks
Storage Area Networks

2. Network Storage
A primary use of networking is to provide shared network storage
In a standard server storage configuration, we typically have a server that contains some type of storage device that is shared so that clients on the network can access the shared storage on the server
This configuration is relatively inexpensive to implement, but it has some serious drawbacks. For example, if the server goes down then the work stations on the network lose access to the shared storage device in that server
One way to fix this is by implementing a storage area network, or SAN

3. SAN Network connections
In a SAN, multiple servers are all configured to share a common storage device. Because they all share the same storage device, a failure of one of these servers doesn't necessarily mean that the data on the storage device becomes unavailable to the client systems
If we implement clustering software, then these servers can take over for one another should one of them go down
To accomplish this, we must have two networks defined. First, we have the standard production network to which all of our workstations are connected using a standard ethernet switch.
The SAN servers will be connected to the same network, allowing them to communicate with the workstations

4. SAN servers Connected to Storage
With a SAN, in addition to our regular production network, we also have a second network implemented
This means that every SAN servers must have two network interfaces installed
The second network, or Storage Area Network, connects each server to the shared storage, But, it does not have any workstations connected directly to it
This means that the servers will sit on two networks. One will carry commands and replies from workstations to servers and the other will carry over commands and replies from servers to storage

5. Targets and Initiators
There are two definitions we need to be aware of when working with a SAN - Targets and Initiators
A SAN target is a storage device
A SAN server is an initiator
Generally speaking, servers will run initiator software to write to and read from targets
All storage area networks will use a network connection to transfer data between the target and initiator

6. Fibre Channel and iSCSI
There are two SAN technologies that are commonly used. The more expensive of the two is called Fibre Channel (FC), and the less expensive option is called iSCSI
FC provides the best performance, while iSCSI costs the least to implement
Regardless of which technology you use, they function in essentially the same way - The Production Network connects the server to the works stations. The SAN network connects each of the servers to the shared storage device

7. Fibre Channel Deployment
To build a Fibre Channel SAN, you need to do the following:
1. Install a Fiber Channel adapter in each server that will access the shared storage on the SAN.
2. Deploy a Fibre Channel switch.
3. Connect each server to the Fibre Channel switch using the appropriate fiber optic cabling for the equipment you are using.
4. Deploy a shared storage device. Typically, this is an external RAID device containing multiple hard disk drives. The array enclosure has a Fibre Channel network adapter implemented that you can use to connect it to the Fibre Channel switch using the appropriate fiber optic cabling.

8. Fibre Channel Protocols
Once physically configured, Fibre Channel uses SCSI protocols to manage the shared storage
The storage devices on the Fibre Channel targets appear to the operating system on the initiators to be locally-attached SCSI hard disks, however, instead of controlling a locally-installed SCSI hard disk, the initiators send SCSI commands over the SAN fabric to manage the remote storage on the target
One key difference between Fibre Channel and traditional SCSI is the fact that it supports multiple initiators. In a traditional SCSI implementation, there is only one SCSI controller (or initiator) on the SCSI bus. This controller manages all devices that are connected to the bus. However, in a Fibre Channel SAN, each server in the SAN fabric is an initiator and can send disk I/O SCSI commands to the shared storage device

9. iSCSI Deployment To create an iSCSI SAN you need to implement:
1. Dedicated Ethernet cabling (fiber optic or UTP)
2. A dedicated Ethernet switch
3. A dedicated Ethernet NIC in each server
4. A storage array that uses a standard Ethernet interface
iSCSI is a network protocol that encapsulates SCSI commands within IP packets and transmits them over a standard Ethernet network. iSCSI is much less expensive to implement because it uses standard Ethernet hardware to create the SAN fabric

10. iSCSI
Because iSCSI uses IP packets, the SAN could be implemented on your standard production network, with all of your other network hosts and devices
However, this is a very bad idea. The performance of the SAN will be heavily impacted because the available network bandwidth would be shared between the SAN and the production network
As a best practice, you should implement a dedicated network infrastructure (cabling, switches, and NICs) that is restricted only to iSCSI SAN traffic. (In much the same way that a Fibre Channel SAN is deployed)

11. iSCSI Protocols
As with Fibre Channel, iSCSI storage devices are targets, while iSCSI servers are initiators
The iSCSI initiator sends SCSI commands within IP packets to the iSCSI target over the network
iSCSI uses port 3260 by default
The storage devices on the remote iSCSI target appear to the operating system on the iSCSI initiator as locally-attached hard disks, effectively creating a SAN

12. FC vs iSCSI
When choosing between iSCSI and Fibre Channel, you should be aware of several factors that may influence your decision:
FC is more expensive and is usually harder to implement than iSCSi. FC requires specialized hardware and knowledge, while iSCSI can be implemented using standard Ethernet hardware and TCP/IP
FC is currently faster than iSCSI. Using Gigabit Ethernet hardware, an iSCSI implementation can approximate the speed of the slowest FC SAN.
FC has a distance limitation of 10km. With iSCSI, IP packets can be routed over many networks, accommodating longer distances. However, performance will be impacted as routing iSCSI packets will introduce latency
Both iSCSI and Fibre Channel provide security features that that can be used to authenticate connections and encrypt data transmissions

13. Clustering Fault Tolerance
Since the servers in a SAN share storage devices, they are commonly deployed in a clustered configuration
With clustering enabled, multiple SAN servers can be grouped together in a cluster to provide a degree of fault tolerance
Because all of the cluster data exists on the shared storage, there's no need to replicate data between servers. To users on the network, the cluster appears as a single file server. If one of the servers in the cluster goes down, the other devices immediately take over and continue to provide access to the files on the shared storage device
This is called a failover, and it usually only takes a second or two to complete

14. Clustering Load Balancing
Clustered SAN servers can also be configured to load balance
If the storage provided by the cluster is heavily accessed by network users, it could potentially create a bottleneck and degrade performance
Using a load-balancing cluster, the network traffic destined for the shared storage can be divided up and distributed between multiple devices in the cluster
This can dramatically speed up performance of the storage system.