This is the first in a series of articles that will, with the insights of key industry players, cut through the hype and jargon surrounding the storage sector to identify the technologies that ISPs can use toward building more efficient and profitable networks.

by Alex Goldman ISP-Planet Associate Editor [July 11, 2002]

The storage industry does have a sense of humor. Any discipline that dubs its basic unit of storage a "JBOD," short for just a bunch of disks, understands that acronyms can be humorous.

Unfortunately, the storage sector has built an industry on a jumble of acronyms that, in practice, make simple technological concepts seem complex or even illogical. Do not fear; we will work our way through the tangle of terminology together because storage is as basic to networks as e-mail service is to an ISP.

What's DAS?
Storage starts with DAS, which stands for Direct Attached Storage. DAS is what your computer has: one or more disks inside the computer chassis. As a common storage method DAS, is not without its problems. The first setback is that DAS leaves a lot of unused storage sitting around. In order to explain why, we'll briefly review how a hard drive stores files.

A hard disk drive attached to a computer needs a certain amount of free space. A hard disk is a platter, like a LP or CD. A computer's hard disk drive uses several platters. In theory, each new file should be saved in a sequential series of data blocks on a cylinder. But in the real world, with data being added and deleted constantly, files get "fragmented," deposited in non-sequential data blocks occupying the gaps left behind by smaller files that have been deleted.

Most operating systems have a utility known as a defragmenter that rearranges files so that they are not fragmented. However, the defragmenter requires free disk space in order to function properly.

The second reason why experts recommend building a storage network is that the need for storage capacity can change rapidly. Imagine that one of your clients' databases is online, and operates through a Web server in your network. The client completes a large sales promotion. The promotion could send enough requests to the server to overload its processor, or it might grow the database enough to fill up available storage space. You would need to upgrade the DAS.

In order to avoid upgrading a DAS system during a crisis, network managers leave a certain amount of free disk space on a hard disk drive, intending to upgrade it before the crisis occurs. Although some high performance applications can require as much as 50 percent of free space on a hard disk drive, reserved space usually runs below 50 percent.

Glenn Clowney, Director of OEM Marketing for Adaptec's Storage Networking Group, says, "many IT managers maintain a 20 to 30 percent buffer in a DAS environment to accommodate future growth." Of course, if there are several users, each with their own directory on a disk, each user will need a separate buffer, and the amount of unused space in this particular case could be 60 percent.

Storage system vendors point to this unused storage space, one-fifth of the total at the very least, as one reason why ISPs should consider building a storage network. As a result, there is a significant amount of unused storage space in an organization operating several hundred hard disk drives. Even upgrading a DAS system when there is no crisis can cause serious headaches.

Balaji Baktha, Adaptec vice president of marketing for storage networking, describes the problems inherent with upgrading a DAS system.

"At some point, you're going to run out of disk space or your CPU will get overloaded," Baktha said. "In order to upgrade the CPU, you may have to change the motherboard and in order to add disk space, you'll have to change the hard drive."

Baktha added that instead of upgrading the machine you have, you might buy an entirely new machine. Either way, this translates into downtime for your network.

"In either case, you have to bring down the network to do this. In a simple business environment, this means that your administrators are doing very important work at night and on weekends and they will require extra pay and still be unhappy," Baktha explained.

ISP businesses are comprised of a significant online component. Baktha contends that even late night downtime may not be acceptable to your customers. Additionally, most ISP businesses don't run on a single server, which compounds downtime for a DAS upgrade.

"In the real world, you'll have several servers, so multiply this problem by x to get a real headache," Baktha added.

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