Moderator: Peter Burris

Analyst: David Floyer

New compliance requirements for data preservation plus the explosion of data volumes has focused attention on backup/recovery (B/R) and archiving applications in the past few years. Inevitably tape, and specifically tape’s access delays (e.g., finding, mounting and spinning up the right tape reel), robot library failure rates and the medium’s sequential read restrictions on B/R and archiving solutions versus its financial benefits, becomes part of that discussion.

Tape’s portability and low cost of operation compared to disk have made it the near-universal choice, particularly for secure, off-site disaster recovery (DR) solutions. In the past few years however, as the cost of drive technology has plummeted and disk systems that keep their drives unpowered until needed, reducing power consumption and heat generation while increasing disk lifetimes, have appeared, systems using disk as a primary B/R and archiving solution have become more visible in the market. Disk, however, still must overcome two major challenges before it can supplant tape for DR:

1. . Disk drives are too fragile to support their transportation to unpowered storage in a secure, remote site, while network bandwidth costs still make backup over the network a very expensive alternative to tape.
2. . Getting full benefit from disk solutions requires a painful, expensive migration to a new, nonstandard B/R software architecture that adds minimal revenue potential to the business.

As a result in the last decade we have seen the emergence of a variety of virtual tape library (VTL) technologies that attempt to address these issues in part by making the disk device look like a tape drive to legacy B/R subsystems. This has two compelling advantages:

1. . Access times are a fraction of those for tape, so a shop can recover newly written data much faster. This is important because a large percentage of restores are made from data that is less than 24 hours old.
2. . VTL libraries can use advanced data deduplication technology to dramatically reduce the need to rewrite unchanged data multiple times in the B/R run.
3. . Despite improvements in mean time between failures (MTBF) for tape drives, the reliability differential between low-cost disk and high-end tape drives is still large enough to merit use of VTL technologies in reliability-sensitive B/R situations.

While some suppliers aggressively push full disk-drive-based VTL products, a hybrid VTL technology combining disk and tape is a superior approach for larger organizations. This can exploit the benefits of VTL on the drive side while still using low-cost, easily transferred tape to meet long-term archiving and disaster recovery (DR) needs. However hybrid application set decisions are complicated by the limited number of products in this category (only a few of the 20-odd VTL vendors offer hybrid solutions off the mainframe) and the emergence of linear tape-open (LTO) based tape systems for large as well as medium enterprise use.

The long-term question is whether tape will remain part of an overall B/R and DR solution. Ultimately we can be sure that low-cost ruggedized disk technologies that support physical removal, truck transport and long-term storage in secure remote sites will appear, while sequential data access will remain a basic limiting factor of tape. Whether those advances will happen this year, or indeed this decade, is an open question. However, until the question of data movement can be satisfactorily answered, tape will maintain an important place in the enterprise. In this environment, hybrid technologies should be getting greater vendor and user attention.

Action Item: Organizations should not overlook the role of tape in B/R and DR applications based on historic concerns of performance, availability and administrative costs. While most VTL vendors are pushing all-disk alternatives to tape, hybrid VTL technologies are the better approach to solving enterprise B/R and archiving requirements in an integrated, flexible and operationally simple packaging.

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