Clustering Concepts Guide
Implementation Considerations > Hardware Comparisons > Network Storage Technologies

Network Storage Technologies

Enterprise storage consolidation is increasingly important because it improves efficiency, decreases redundancy, and simplifies management.

The two most significant storage technologies currently used are Network Attached Storage (NAS) and Storage Area Network (SAN). Many of the previously existing differences between the two primary network storage products (traditional NAS and SAN storage solutions) are no longer relevant.

Instead, the main differentiation between NAS and SAN products is the choice of network protocol. Although both NAS appliances and SANs provide enterprise storage and offer storage consolidation, they also present different services, advantages, and limitations that need to be considered when designing the system architecture.

Summary of NAS / SAN Features / Capabilities

The following information summarizes the similarities and differences in NAS/SAN capabilities. See Comparison Summary: NAS/SAN for a comparison table of features.

Network Attached Storage (NAS)

A Network Attached Storage (NAS) system is single-purpose, dedicated file sharing device that attaches to the LAN, just like any server or workstation. With a NAS device, storage is not an integral part of the server. In fact, a NAS device does not need to be located within the server but can exist anywhere in a LAN and can be made up of multiple networked NAS devices.

Rather than containing a complete operating system, it is specifically designed to process only file reads and writes. A NAS has a proprietary file system and can serve files across platforms because it can read all major file systems. Because NAS appliances have the ability to share a data instance on multiple application servers, they are excellent cross-platform, collaborative tools.

NAS devices do not provide typical server-centric activities such as e-mail, authentication or file management. Instead, in the storage-centric design using a NAS device, the server still handles all of the processing of data but a NAS device delivers the data to the user. Note that although the capacity of a large NAS appliance can be in the terabyte range, it is still subject to the variable behavior and overhead of a network that may contain thousands of users.

Adding or removing NAS devices is similar to adding or removing any node in a network and can be accomplished without shutting the devices down for maintenance and upgrades.

Using traditional LAN protocols such as Ethernet and TCP/IP, the NAS enables additional storage to be quickly added by plugging it into a network hub or switch.

Storage Area Network (SAN)

A Storage Area Network (SAN) is a high-speed, multi-storage network that connects multiple servers to a centralized pool of shared disk storage devices (machines that contain nothing but a disk or disks for storing data). A SAN’s architecture works in a way that makes all storage devices available to all servers on a LAN or WAN. As more storage devices are added to a SAN, they too are accessible from any server in the larger network.

Each server on the network is directly connected to the SAN and treats its allocated storage space like a directly-connected disk. Because of the direct connections to every server, the SAN model acts as a secondary network to the LAN. As such, this secondary network relieves the main network of massive data transfer loads because backup traffic occurs between storage devices inside the SAN.

SANs allow sharing the storage infrastructure without implying data sharing. This allows higher utilization of storage devices and easier reconfiguration than is possible with direct attached storage. SANs provide storage allocation flexibility through repartitioning and management tools. When storage space must be reallocated from one server to another, the SAN can simply be repartitioned. And, because stored data does not reside directly on any of a network’s servers, server power is utilized for business applications and network capacity is released to the end user.

Compared to managing hundreds of servers, each with their own disks, SANs improve system administration. By treating all the company’s storage as a single resource, disk maintenance and routine backups are easier to schedule and control. In some SANs, the disks themselves can copy data to other disks for backup without any processing overhead at the host computers.

The SAN network allows data transfers between computers and disks at the same high peripheral channel speeds as when they are directly attached. SANs can be centralized or distributed. A centralized SAN connects multiple servers to a collection of disks, whereas a distributed SAN typically uses one or more switches to connect nodes within buildings or campuses. Note that the channel-attached SAN must be taken offline to reconfigure it.

Note: SAN environments can be used with Windows but restrictions on the use apply; contact Consulting Services before implementing a SAN in a Windows environment. UNIX-based Content Server clusters only work in SAN environments using third-party cluster software to virtualize the volume.

Comparison Summary: NAS/SAN

The following table summarizes NAS/SAN systems: