SAN/NAS

As companies rely more and more on e-commerce, online transaction processing, and databases, the amount of information that needs to be managed and stored can intimidate event he most seasoned of network managers. While servers do a good job of storing data, their capacity is limited, and they an become a bottleneck if too many users try to access the same information. Instead, most companies rely on peripheral storage devices such as RAID disks, optical storage systems, and even tape libraries. These storage devices are effective for backing up data online and storing large amounts of information.

But as server farms increase in size, and as companies rely more heavily on data-intensive applications such as multimedia, the traditional storage model isn't quite as useful. This is because access to these peripheral devices can be slow and it might not always be possible for every user to easily and transparently access each storage device.

Recently, a number of vendors from all walks of the industry have been pushing a concept called a storage area network (SAN). SANs provide more options for network storage, including much faster access than network attached storage (NAS) and the flexibility to create separate networks to handle large volumes of data. This is the basic concept of a NAS. NAS is straightforward in that disc arrays and other storage devices connect through the network through a traditional LAN interface such as ethernet. Storage devices attach to network hubs much the same as servers would.

NAS makes storage resources more readily available and helps alleviate the bottlenecks commonly associated with access to storage devices. However, NAS does have a few drawbacks. First, network bandwidth places throughput limitations on the storage devices. Most NAS servers are placed on 10 or 100 meg/sec ethernet LANs, but even if a network is running at gigabit speeds, most NAS vendors today only offer interfaces up to Fast Ethernet. Another downside to NAS is the lack of cohesion among storage devices. While disc arrays and tape drives are on the LAN, managing the devices can prove challenging since they are separate entities and are not logically tied together. NAS has it's place as a viable storage architecture, but larger enterprises require something a few steps beyond. Large enterprises that want the ability to store and manage large amounts of information in a high performance environment now have another option, the SAN.

In a SAN environment, storage devices such as RAID arrays are connected to many kinds of servers via a high-speed interconnection such as fibre channel. This setup allows for any-to-any communication among all devices on the SAN. It also provides alternative paths from server to storage device. In other words, if a particular server is slow or completely unavailable, another server on the SAN can provide access to the storage device. A SAN also makes it possible to mirror data, making multiple copies available. The high speed interconnection that links servers and storage devices essentially creates a separate external network that is connected to the LAN but acts as an independent network.

There are a number of advantages to SAN and the separate environments they create within a network. SANs allow for the addition of bandwidth without burdening the main LAN. SANs also make it easier to conduct online backups without users feeling a bandwidth pinch.

When more storage is needed, additional drives do not need to be connected to a specific server. Rather, they can simply be added to the storage network and accessed from any point. Another reason SANs are making big waves is that all the devices can be centrally managed. Instead of managing the network on a per-device basis, storage can be managed as a single entity, making it easier to deal with storage networks that could potentially consist of dozens or even hundreds of servers and devices.