Disk- or tape-based backup, or both?

Posted on May 01, 2003

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Speedy disk backup is gaining popularity as networking demands increase, but traditional tape-based data protection won't disappear overnight, so consider combining the best of both.

By Phil Roussel


Phil Roussel
Arkeia
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With more and more pressure on IT administrators to protect data and make it readily accessible 24 hours a day, an increasing number of companies are looking for alternatives or supplemental solutions to traditional client-to-tape backup and restore.

Faced with budget constraints and a steadily escalating need for quick, if not instant, data recovery, disk-to-disk backup is an option that some businesses have implemented, and many more are considering. But comparing disk backup to tape backup isn't really an exercise in which method is "better." More realistically, the comparison should be based on what is most appropriate based on networking demands and structure.

Historically, tape has been the preferred backup method because tape cartridges were inherently cheaper than disk drives. A secondary reason was that tape cartridges were portable and could be stored away from the computer systems.

However, technology evolves to meet demands. Disk drive prices continue to plummet—particularly in the case of ATA drives—resulting in a competitive option to pure tape backup systems. Of equal significance is the fact that tape is comparatively slow (because it relies on sequential access), sometimes making it difficult to find files quickly. Disk drives, on the other hand, use direct random access and read/write efficiencies that translate into enhanced productivity and potentially lower operating costs.

Industry professionals who tout disk-to-disk backup/recovery options point out advantages that are primarily related to instant access of mission-critical information. They claim

  • Much shorter backup windows with little or no downtime;
  • Rapid restore; and
  • Cost effectiveness.

Users and servers are increasingly scattered across wide-ranging time zones, which requires applications and data to be available 24¥7. For data to be unavailable during a backup window of significant duration is no longer just inconvenient: It is unacceptable. In highly competitive situations, businesses of all sizes need up-to-the-minute data protection without sacrificing high availability.

Disk-to-disk backup can shorten or eliminate some backup window problems. Simply put, writing straight to disk is faster than writing to tape. Down time is reduced or eliminated, thus decreasing the time when data is vulnerable to loss.

Similarly, restoring data from disk drives is quicker than from tape. Instant access to files is possible for everyone on the network, without a time-costly restore of huge tape archives.

The cost difference between disk and tape is narrowing, with disk-based hardware prices at an all-time low. When considering speed and capacity ratios, hard disks can offer an impressive return on investment.

While tape has historically been substantially less expensive than equivalent disk storage, disk prices have fallen dramatically (and capacities grown) to the point where disk-based systems have become a financially feasible alternative to tape-based systems while delivering significantly superior performance.

On the other hand, tape backups are still easier to secure, either by archiving to a different site or simply by pulling the tape each night and taking a copy home. Disk arrays just are not as flexible when formulating security guidelines.

In actuality, however, the combination of disk and tape backup may be the optimal solution for many businesses, especially if there is an ongoing need for quickly retrieving and restoring files. In this approach, data is backed up to a hard drive, giving users immediate access to the previously saved files. Meanwhile, the disk array is backed up offline to archive the files as they change. Users don't lose any working time, and data isn't vulnerable for long periods of downtime. The tape drives can be at a different location or can be duplicated by tape management software in order to take copies off-site.

Essentially, then, the question of "Is disk or tape backup best?" isn't as valid as "What's right for my configuration and network demands?"

Phil Roussel is CEO of Arkeia (www.arkeia.com)in Carlsbad, CA.


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