Feature

Storage architecture choices: SANs

By Yuval Shavit, Features Writer

Storage area networks (SANs), which were once available only to large enterprises that could afford to pay steep premiums for the best storage, are increasingly moving downstream. SANs combine the benefits of shared storage with those of direct-attached storage (DAS), and newer technologies make them affordable even for small businesses. This article will explore why storage area network (SAN) devices may be right for your clients.

Storage acronyms: SAN, NAS and DAS

The three main ways of connecting storage to servers are SANs, network-attached storage (NAS) and DAS. With DAS, which is the most basic form of the three, the drive connects directly to the server and is often even in the same enclosure. Because DAS is simple to install and requires no large, IT-level planning, it's still what many small businesses rely on, said Paul Franco, executive vice president at Zibiz Data Management, a storage consultancy in Ronkonkoma, N.Y.

SANs and NAS both separate data storage from servers, allowing servers to share those resources. NAS devices have their own file system, so they work best as file servers. SANs give block-level access and appear to computers as normal drives, so they work better for applications such as databases. Companies start needing databases once they reach about 100 users, which is why even small businesses are starting to look into storage area networks, Franco said. SANs are often faster than NAS systems, too.

Benefits of SANs

Why storage area networks? Depending on how many servers your client has, a SAN can offer significant advantages over a DAS array for each server. Consolidating storage devices will save your clients money by allowing them to buy capacity according to what the entire company needs, as opposed to having each server work with its own disk array, much of which may go unused. Provisioning tools can let your client dynamically allocate space -- instead of giving a server 10 GB in anticipation of growth in five years, an IT manager can give it 2 or 3 GB and increase that as needed, Franco said.

Because SANs can consist of several physically separate drives or arrays, they also offer replication and disaster recovery features. For instance, you can set up two SANs with automatic, real-time replication. If the primary SAN goes down for any reason, the system will automatically fail over to the second.

SANs also complement server virtualization. One of the features of some virtualization software is the ability to move images between physical servers on the fly, without downtime. This requires the two servers to share the same storage device -- both so they can access the same data and to serve as a medium for the virtual machine (VM) image.

Cost of SANs

A traditional SAN works on a Fibre Channel (FC) network. The wires may be either fiber-optic or copper, but since even the copper FC wires are different than Ethernet cables, all FC-connected SANs require a separate, dedicated network.

Fibre Channel equipment is expensive; the wires, which are often optical, can cost $100 to $200 each, and each server's FC adapter will cost another $400 to $1,000, said Henry Baltazar, storage analyst for The 451 Group in San Francisco. This extra infrastructure makes up the bulk of the cost for SANs that use FC, which is why storage area networks have traditionally been reserved for larger companies while smaller companies have had to go sans SANs.

But iSCSI, a variant on the SCSI interface that runs over IP, can eliminate those costs by connecting your SAN devices over your existing LAN. Your client will still need to make a few adjustments, such as configuring a virtual LAN (VLAN) for the SAN drives to ensure that they get all the bandwidth they need; your role should include helping the client with this implementation work. An entry-level iSCSI-attached SAN can cost as little as $10,000 and are typically easy enough to self-configure, Franco said.

In the next installment of our Hot Spot Tutorial on SAN design services, we'll take a closer look at the comparison between Fibre Channel and iSCSI, as well as a new technology, Fibre Channel over Ethernet (FCoE), that's on the horizon.

 


This was first published in December 2008

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