Taking the best of tape and disk

Despite its relatively slow speed and overall bulkiness, tape has its strengths. After all, it's inexpensive compared with most disks, it's portable and has been used in data centers for years.

Still, traditional tape back-up systems have begun to wear out their welcomes at some companies, which are turning to virtual tape technologies.

Virtual tape -- or tape emulation -- combines traditional backup methodology with inexpensive disk drive technology to create a disk-based library that acts as a tape library. In concert with traditional back-up software from vendors such as Commvault Systems Inc., Legato Systems and Veritas Software Corp., virtual tape products write data to disk in current tape formats. Because disk is used rather than tape, data can be backed up at channel speeds many times faster than with tape and also recovered more quickly. With this technology, IT staffs no longer need to mount, position and dismount tapes or worry about the reliability of the media.

As an IT executive at e-commerce and payment services vendor FirstData Corp., Todd Cushing had no illusions about his company's data storage needs lessening any time soon. Neither did he think that the Omaha company's tape-based storage system was the answer.

FirstData turned to virtual tape technology, replacing 74 tape silos and 1,500 tape drives with seven virtual tape storage systems to back up 60TB of data on nine mainframes. FirstData uses Storage Technology Corp.'s Virtual Storage Manager appliances, which compete in an increasingly crowded market against products from established players such as EMC Corp. and Quantum Corp. and newcomers such as Diligent Technologies Corp. and Sepaton Inc.

"Using [virtual tape libraries] rather than tape has saved us thousands of square feet in our data centers," Cushing says.

FirstData had been doing a lot of what Cushing calls "tape stacking." In other words, it had been converting oodles of tapes from one format to a common format to replace aging media and bring consistency to the operation. The process proved labor-intensive and was prone to errors, he says.

Cushing says FirstData is mulling whether to use virtual tape technology for its Unix and Windows NT systems as well, which require about 12TB of data backup. While these systems aren't as inefficient when it comes to tape backup, they probably still could benefit from virtual tape's reliability and speed, he says.

Virtual tape evolves

The concept of virtual tape systems isn't new, as IBM Corp. introduced the idea for its S/390 mainframes in the mid-1990s. The company's IBM 3494 Virtual Tape Server was meant to take the place of numerous bulky 3494 Tape Libraries and save floor space, improve tape utilization, reduce tape mounts and improve performance by eliminating the physical movement of tape. StorageTek and Fujitsu Siemens Computers (Holding) BV subsequently introduced their appliances for mainframe environments.

"On the mainframe, the process of writing data sets to tape often left the tapes with a lot of empty space," says Dave Hill, senior analyst with Mesabi Group. "With virtual tape, multiple data sets are concatenated on disk and then written to tape," thus achieving better utilization.

The advent of inexpensive Serial Advanced Technology Attachment (ATA) disks has made virtual tape libraries an affordable alternative to tape backup, proponents say. While the ATA drives that most appliances use are not as inexpensive as tape, their reliability and speed of recovery make them competitive.

Virtual tape appliances fit in the network between file and media servers and the back-end storage-area networks (SAN) and tape libraries.

Andrew Ferguson, manager of enterprise operations for Brookhaven National Laboratories in Upton, N.Y., chose a virtual tape library appliance from Sepaton to back up a Windows network environment. Before using Sepaton's S2100-ES, the Brookhaven network consisted of multiple, separate backup environments such as for Microsoft Exchange and for database servers.

"We wanted to get these islands of backup under one enterprise product," Ferguson says. "We also wanted to centralize our tape changers."

Sepaton's offering looks like a tape library but is a lot faster, says Ferguson, who backs up 17TB of data from a Dell/EMC SAN.

Virtual tape and tape libraries will supplement traditional tape technology over the next few years, according to Alex Gorbansky, an analyst at Taneja Group.

"Tape is going to continue to have a role as nearline and long-term archival media," he says. "As people will start to maintain more data online, virtual tape will start to eat into some of tape's capability as a nearline repository."

Brookhaven's Ferguson has adapted his tape backup for just that use.

"We now go to tape only if we need to for archiving or if for some reason we need to take a tape out of the environment and do a restore into another environment," he says.

Some virtual tape library packages such as Advanced Digital Information Corp.'s Pathlight VX, Fujitsu Siemens' CentricStor and Neartek Inc.'s Virtual Storage Engine already include provisions for migrating data from the disk-based virtual tape system to tape. These offerings don't require IT to use backup software to copy data from the virtual tape system to a physical tape library and then to tape without involving the media server.

This story, "Taking the best of tape and disk" was originally published by Network World.

Copyright © 2005 IDG Communications, Inc.

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