Storage Architecture

Storage Area Network

The second type of networked storage is called storage area network (SAN). The major limitation of DAS is a limited number of devices can be attached to the server. NAS appliances are limited by their role and network backups are limited by the consumption of network bandwidth. These limitations are addressed in a SAN.

A SAN provides a powerful framework for building and managing storage systems that are flexible and cost effective. A SAN utilizes a combination of hardware and software working together in concert to provide a high-performance and scaleable solution for storage needs. A SAN contains a dedicated network of storage devices. This consolidates the storage devices and removes them from the main LAN. Storage devices can be tape, disk, or both. Backups that occur in the SAN do not affect network bandwidth. A SAN can also be configured to be fully redundant containing no single point of failure.

This image shows a generic representation of a storage area network

SAN Hardware

Typically a SAN will be comprised of the following hardware:

At least one Fiber Channel HBA per server(two for redundancy)
At least one Fibre Channel switch (two for redundancy)
One or more storage device
SCSI to Fibre bridge for SCSI tape drives

Fibre Channel HBAs are installed into the servers allowing them to communicate with Fibre devices. While either copper or optical HBAs can be used in a storage area network, only optical HBAs are used in a Dell | EMC SAN. Fibre Channel cables connect to a Fibre Channel switch providing the connection point for all Fibre devices in the SAN. To ensure full redundancy, two switches are needed. SCSI devices such as tape drives can interface through the SAN using a SCSI-to-Fibre Channel bridge.

SAN Redundancy

In a SAN environment, each component also has a redundant backup configured to have a failover path in the event of a component failure. In the event of a failure, the component's functions can continue to be completed. Component failures are transparent to users.

DAS NAS SAN

Primary Function SCSI or Fibre Channel disk enclosures attaching directly to a server to provide storage expansion. Access to files is through the LAN/WAN. Specialized appliance providing consolidated networked file services for clients and servers. Storage is accessed directly across a LAN/WAN. Provides consolidated Fibre Channel storage for servers. Storage is accessed across a dedicated storage network.

Installation Can be installed easily, but the server must be brought down to install. Can be installed quickly and easily without downtime. Installation can be complex.

Scalability Limited number of disk enclosures can connect to a server. Multiple NAS appliances can be added to the network. Storage can be scaled by adding additional Fibre Channel switches and storage devices.