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Get the Most From Your Storage Investment
Providing adequate storage doesn't take an army of servers. Reduce your total cost of ownership with the proper use of NAS and SANs.
by Tom Clark

May 2003 Issue

For This Solution: Host adapter cards, Windows drivers, NAS appliances, SAN switches, SAN-enabled storage arrays and tape backup devices

I once visited a major computer processor chip manufacturer that has more than 7,000 servers to manage. This company requires a small army of administrators to manage its corporate storage assets, because each server has its own direct-attached storage. When disk storage on an individual server reaches capacity, the IT department must deploy yet another server with additional storage to accommodate more data. Adding more servers and storage in turn requires hiring additional administrators, swelling the ranks of the IT staff further and putting enormous pressure on an already tight IT budget. Managing and backing up data securely from thousands of individual servers is an enormous problem.

Although this scenario represents an extreme case of unplanned storage acquisition, many IT managers feel pinched between the rock of fixed budgets and the hard place of ever-growing storage demands. Continued server deployment and direct-attached storage lead inevitably to higher administrative overhead, and many IT departments simply don't have the personnel or funding to keep up. In this article, I'll look at some of the new shared-storage technologies that enable IT managers to manage data storage more efficiently. Network-attached storage (NAS) and storage area networks (SANs) are two distinct approaches to fixing the same problem: managing more data with fewer administrators. By understanding what NAS and SAN solutions can do for you, you can deal proactively with storage issues while reducing your total cost of ownership over time.

Defining Shared Storage
Shared storage is a radical departure from the traditional server/storage relationship. In a conventional server/storage configuration, servers equipped with Small Computer System Interface (SCSI) adapter cards use parallel cabling to connect to storage arrays or tape-backup devices. This direct-attached storage model binds each server to its own storage resources. The failure of a server results in loss of data access, because the server is the exclusive owner of its storage devices. Loss of data access causes revenue loss for most companies, and more money is lost the longer a server is down.

Also, each server can support only a fixed number of storage devices. An individual server's total capacity might be reached at some point. The administrator needs more storage capacity, but—in the direct-attached storage model—acquiring more storage capacity means acquiring another server as well. The new server represents a substantial hardware and software investment, because it requires an operating system, applications, and device drivers. Because the new server is the exclusive gateway to its attached storage, it must be managed individually to monitor storage utilization and to perform tape backups. Consequently, some servers might have underutilized storage capacity, while others nearly exceed capacity. This makes it extremely difficult for IT managers to exploit their total storage assets fully and bring costs under control.

Shared storage cuts the thick umbilical cord of SCSI cabling and the exclusive ownership of storage by individual servers. You accomplish this by connecting servers and storage separately in a peer-to-peer network. Networked storage allows multiple servers to share storage arrays and tape subsystems. The failure of an individual server no longer results necessarily in loss of data access, because no server owns the storage exclusively. In the event of server failure, administrators can assign another server to the storage resources of the failed unit. As a result, shared storage facilitates applications, such as server clustering, that reassign storage connectivity over the network automatically and provide high-availability data access.