AIX > Storage > Disk

Backup and Archiving Media Madness


Five years ago, it was unheard of to suggest replacing tape media with disk for backups and archiving in a data center environment. Now I find myself lecturing in rooms full of people on the potential merits of using disk for those same functions; 72 percent of those surveyed are interested in using disk somewhere in their backup environments, a solid indication that disk has made significant inroads and isn't just another fad.

Why the rush to dump the tried-and-true technology of tape media for its spinning cousin? Did the 72 percent surveyed suddenly realize that tape is bad and disk is good? And what about the 28 percent not considering disk? What do they see in tape over disk? Let's start with why people want to leave tape.

Does Tape Get a Bad Rap?

Tape's reliability concerns most customers. It's every IT manager's nightmare: During a data-center recovery, the one tape containing the organization's most critical data is corrupted and can't be read. Imagine deleting or breaking the only VHS tape of your wedding day. Now picture needing that tape to run your household and you can understand the nightmares of those poor IT managers. Although some enterprise-class backup software products such as IBM* Tivoli* Storage Manager minimize this exposure with processes that constantly recycle and refresh the tape volumes, the possibility of corruption remains a major drawback in relying on tape media.

Many also consider tape technology old and say it can't be a viable solution to modern problems. Indeed, tape technology recently celebrated its 50th birthday, but consider that the first true disk drive, the IBM 3340 Winchester sealed hard disk drive, was created in 1973. While neither technology is a new kid on the block, neither is ready for retirement. Both technologies are constantly being improved and new performance and capacity thresholds are being achieved on a regular basis. IBM's TotalStorage* Enterprise Tape Drive 3592 J1, which offers a native data transfer rate of up to 40 MB/sec and tape volume capacities of up to 900 GB (with 3:1 compression), is just one example of new tape technology. As long as tape technologies continue to advance, tape will remain a viable solution.

Two legitimate discrepancies between disk and tape that concern users are the difference in cost and the speed of disk for restoring a system versus that of tape. Disk prices have dropped steadily for years, but in the last few years they've plummeted, raising the argument that disk is almost as inexpensive to use as tape. Advanced technology attachment (ATA) serial disk arrays like IBM's FAStT storage servers have come to the forefront as viable, low-cost alternatives to tape.

Backups Without Tape

Many IT departments that steadfastly perform backups lose sight of the fact that backups are primarily performed to allow restoration of deleted data or recovery of an entire system. These types of restores are requested frequently--often enough to discomfit any CIO--and missing data needs to be recovered quickly. This is when having a disk-based restoration method is most beneficial. The data you need to restore is readily available on disk and can be accessed faster than if it resided on tapes. You also eliminate the time required to search the automated tape library for the tape volume, mount and dismount the tape media and search the individual tape volumes for the data to be restored. Combined, these factors can dramatically reduce restoration time.

Sending backups to disk instead of directly to tape is usually beneficial and supported by some industry-leading, enterprise-class backup software products, such as IBM Tivoli Storage Manager. Staging backups on disk before migrating the data to tape allows faster restores by caching the backup data in disk storage pools. Traditionally, the IBM Tivoli Storage Manager storage pool hierarchy model migrates the data in these pools to a primary tape storage pool, usually referred to as the onsite tape storage pool. The onsite storage pool is then backed up to a copy, or offsite, tape storage pool. Figure 1 illustrates this double-backup hierarchy.

Stephen Firmes is a senior engineer with SEPATON, Inc. Stephen can be reached at sfirmes@sepaton.com.


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