Up the SAN-Box - storage area networks take off - Statistical Data Included

Emedia Professional, July, 1999 by David Doering

We could see increased capacity for the discs eventually, but it won't happen anytime soon. Current laser technology stands at 780nm for CD recording and 650nm for DVD. To improve density, we need to improve lasers to the 440-450nm range (the so-called "blue" laser). What does this mean to density? The blue laser recording would increase capacity by four times--making a single DVD-RAM disc support 37.6GB double-sided. That would make it a definite contender against tender tape.

If we want to go beyond that, though, we run into a few problems. Even if lasers improve, disc capacity will still hit the wall when we reach the limitations of the plastic substrate used in the discs. At about 300nm and lower, the plastic itself is no longer transparent--requiring some new substrate technology to replace plastic--a significant barrier to the extensive (and expensive) installed base for manufacturing media.

Another drawback to decreasing the wavelength, and thereby increasing density, comes from heat. As lasers go from red to blue (650nm down to 440nm), the temperature of the laser almost doubles--from 30 degrees Celsius to 50 to 60 degrees. Granted, the increased temperature is low compared with Intel's egg-cooking Pentiums, but it isn't the interior temperature that's the problem. Trouble is, the hotter temperature means a shorter life span--40 percent shorter. Today's recorders average 5,000 to 5,500 hours between drive failures. A blue-laser-equipped recorder might only last 3,000 to 3,500 hours.

For a standalone recorder, this may be acceptable. It is a deal-killer for a network.

BACKUPS WITHOUT HICCUPS

Another drawback to enterprise backup and archiving using contemporary optical technology is speed. Seagate, for example, boasts that its Backup Exec for NT is capable of handling up to 28MB per minute. This respectable rate is quickly diluted with today's hard disks--as it would take one full hour to back up a small 1.5GB hard drive--and that at its maximum speed. On a network with 100 to 500GB of storage, a few servers would take a battery of such recorders to keep backup time to a minimum.

Granted, a SAN-attached optical backup or archive system doesn't fall prey to the shrinking backup window. Today's network no longer has a "down" time. In the 1980s and early 90s, when 5:00 hit, most workers went home. By midnight, the network was quiet--perfect for the administrator to run backup. In 1999, that's no longer the case, as the Internet now makes the corporate data-information, base, sales information and electronic commerce open for business 24-hours a day. So when can a lengthy backup session occur?

With a SAN, backup can occur at any time, since it adds no burden to the network. But the latency problem remains for optical versus tape backup. By the time a large array of DVD- or CD-R drives completes their backup cycle, the data is dated much older than the contents of a tape backup. How much more will it cost to reconstruct the lost data in the event of a system failure using a 120mm system versus a tape backup program?