Dec 31 2009

Tale of the Tape

A virtual tape library can ease data storage and access management.

It seems like only yesterday that data protection meant backing up your data to tape, perhaps once per day, once per week or even once per month — if the data wasn’t particularly critical.

This has changed almost overnight because of new storage technologies such as deduplication, intelligent switches, virtual tape libraries (VTLs), continuous snapshot, continuous data protection (CDP), storage virtualization software and distributed remote office/branch office (ROBO) to disk.

Sifting through these disk-based storage options can be puzzling. The newer technologies — deduplication and CDP — seem especially promising and may eventually eclipse the more tried-and-true virtual tape systems. Even so, VTL remains among the most efficient and cost-effective choices for storage administrators, says Nancy Roper, a consulting IT specialist in the IBM Americas Advanced Technical Support group.

VTL technology may not be as flashy as some of the others, she says, but it is time-tested and proven. Almost 30 vendors — including Copan, EMC, Fujitsu Siemens, Hewlett-Packard, IBM, Overland Storage and Sun Microsystems — support these disk systems.

Virtual tape creates new options for shortening backup windows, says Fred Moore, president of Horizon Information Strategies, an information strategies consulting company in Boulder, Colo. VTL systems provide faster backups because they can run concurrent and parallel saves without the need for additional physical tape devices, he says. It can also reduce the impact of media errors during the saves and hardware problems on the physical tape devices. The virtual use of the devices also allows for ad-hoc onsite restores rather than recalling duplicate offsite tapes.

VTLs make it possible to save data as if it were being stored on tape, although it may actually be stored on hard disk or another storage medium. Multiple disk arrays are pooled together into what appears to be a single storage resource to administrators.

This is the approach taken at the Agriculture Department’s National Information Technology Center, which has adopted virtual tape to support users in USDA bureaus. The center cites a reduction in lost or corrupted data as a primary benefit for users. The redundant arrays of independent disks subsystem at the center can emulate 128 tape transports.

Moore notes that disk arrays not only look like tapes, but they can also be man­aged as a single, logical entity, regardless of the storage medium being used.

But potential users need to be aware of the distinction between integrated and standalone VTLs, he says. “An integrated VTL combines disk arrays as a front end to an automated tape library, whereas a standalone does not directly control the physical tape library.”

A standalone system may be suitable for smaller organizations not requiring management of a huge pool of data, while an integrated system would be advisable for large organizations managing many terabytes of information, Moore says.

Weighing the Benefits

Storage experts maintain that disk-based backup solves the problems that have been plaguing conventional tape-based backup for decades.

As to VTL benefits, Roper and Moore point to:

  • Lower operating costs. The capacity of disks is growing exponentially, with concomitant price drops. In many cases, concurrent or parallel backups may be run without buying more drives.
  • Faster data recovery. The random search capability of disk-based systems enables speedier recovery and decreased downtime.
  • Possible backup performance increases. Virtual tape saves typically run at speeds comparable to save files when they’re on a system with adequate resources.
  • Elimination of some save-file restrictions.
  • Reduced impact of media errors. Disk systems are less prone to error than tape systems.
  • Increased user confidence. Users trust features such as RAID and other high-availability options available from disk-based systems.
  • Increased reliability. RAID disks are more reliable than tape.

The Cost Factors

Should you move to virtual tape backup now, or wait until more advanced virtual tape systems come along?

If costs are your main concern, don’t wait. An EMC/Legato report, “Disk-Based Data Protection: The New Data Backup and Recovery Imperative,” shows that disk-based VTL backup can save big bucks. Organizations using tape backup will endure about 30 days of systems backup downtime per year. Disk backup improves this statistic by 30 percent. That’s nine days per year saved from using disk backup with or instead of tape backup.

How expensive is downtime? It depends on the organization, but the Meta Group of Stamford, Conn., estimates that in a large enterprise, the average cost of downtime as a function of idle labor can amount to more than $1 million per hour.