Tape turning: protect against data loss

Computer Technology Review,  Dec, 2004  by Rich Harada

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Using disk to replace tape for backup and disaster recovery operations is one of the big stories in the data storage market this year. On the surface, the idea makes sense: disk is well-understood, fast, reliable and inexpensive--or at least that's what the VTL (Virtual Tape Library) and D2D (Disk-To-Disk) marketers promise. But many users have taken a look at disk-based data protection options and come to the conclusion that they aren't ready for prime time, at least not yet. They seek to improve the costs and efficiency of their data protection systems, but some issues are keeping them from doing so:

* Disk hardware costs more than both tape hardware and tape media, a lot more. Even low-priced ATA-based drives are several times the cost of tape, on a capacity basis.

* Disk-based solutions do not provide an easy, cost-effective way to store a copy of your data off-site; you either need to replicate the data to another disk-based system in another location (over expensive transmission lines) or use a local tape system to enable off-site transport and storage.

* Add in the electricity and cooling costs of all those spinning disks, plus the costs of scaling to higher capacities, and you're looking at a significant investment; and the pay-back is only seen in somewhat faster recovery times.

* Some users have problems with volume labeling compatibility when they use both disk and tape.

It seems strange to some to use "cheap" disk to protect the data on "expensive" disk. If the ATA disks in the VTL or D2D systems are reliable enough for a data protection solution, why aren't their high-end SCSI and FibreChannel cousins reliable enough to avoid the need for backup in the first place? Actually, by adding more magnetic disk into the system, aren't you just adding more opportunity for data loss?

"While disk has received a great deal of attention lately as a backup-and-restore media, it should not be viewed as an all-out replacement for tape," says Dianne McAdam. Senior Analyst and Partner of Data Mobility Group. "Rather, it should be viewed as an addition to existing backup processes. In fact, D2D should be considered as part of a larger backup strategy of primary disk to secondary disk to tape, or D2D2T. While disk can be used to store the most current versions of backups, tape continues to maintain its place in the data center for retention of long-term backups and archival storage. And tape storage costs much less than the equivalent amount of disk storage. Not only does disk storage initially cost more than tape, but continues to costs more throughout its life when environmental factors such as power, cooling and floor space costs are added to the equation."

So, if you think that a disk-based data protection solution might not be right for your company, the next best thing is to improve your tape operations to reduce or even eliminate the problems that may have gotten you to think about a disk-based solution in the first place. The hearsay issues with tape include reliability, performance, and utilization. Let's take a look at approaches to improve each of them.

Reliability

Today's professional tape systems are designed to provide robust and reliable data storage for many years. Even so, there are several factors that feed into the perception that tape is inherently unreliable. As with anything, one of the primary factors is human error: most data recovery failures are due to a failure to perform the backup in the first place.

"Automate data protection programs as much as possible to eliminate the
chances for human error. Document the process and periodically review it
for opportunities to improve."
--Dawn Wortman, Fujifilm

The second most-common failure factor is from improperly handling tape media. When transported in its original packaging, and stored in a controlled office environment, professional-grade tape will reliably retain data for at least 15 years--far longer than almost any data protection or archival application requirement.

"Follow the manufacturer's recommendations for tape handling and
storage. Excessive heat or humidity will reduce the life and reliability
of magnetic tape."
--Jim Milligan, Imation

Data errors and other problems can occur if the tape drive is not maintained correctly. The most important aspect of maintenance is periodic cleaning of the read/write heads. Many drive formats use a special cleaning cartridge to perform this operation automatically, and some drives even prevent writing new data if they have gone too long without a cleaning cycle.

"Ensure that cleaning cartridges are only used for their recommended
number of cycles and that other maintenance schedules are followed, per
manufacturer's recommendation."
--Paul Scheuer, IBM

A growing source of tape problems is due to the use of recycled tape cartridges. As with buying any used products, you may be purchasing someone else's problems and in the end, will not be saving money by using recycled media. You never know how these tapes have been used, handled and transported, or even what source of media may be in the cartridge.