Disk-to-disk backup is one of the hottest technologies in storage right now, but as it makes its way into production environments, some users are discovering problems.
Oswald D'Sa, vice president of technical operations at Claria Corp., a small marketing company based in Redwood City, Calif., recently purchased a tape library from StorageTek Corp. after writing off most of the disk-to-disk backup products on the market.
"Disk-to-disk is not complete as of now. There's one feature ... done well in each of them, but no single product with everything," he said.
In most scenarios today, users still want to archive their data on tape, to get it off site. But according to D'Sa, there is a lack of synchronization between the media and volume labeling on the tape and disk systems that leads to conflicts over which data gets written where.
"The compression ratios have not been well integrated between disk and tape, which means users have to buy a large amount of disk to ensure they don't run out of space," D'Sa said. "I don't want to spend the money until the appropriate cataloging is there … until Legato or Veritas takes care of this integration."
Many of the new disk-to-disk backup systems are proprietary, which turned off another user in the banking field, who requested anonymity. He was reluctant to get locked into another vendor and also wary of the management costs associated with disk-based backup products. "You pay a few cents less for SATA drives, but it's another technology which requires training and maintenance and another human body to manage … it's expensive," he said.
Dianne McAdam, senior analyst and partner with the Data Mobility Group, based in Nashua, N.H., warned users not be taken in by the cheaper up-front costs of SATA for disk-based archiving, as other hidden costs actually make it an expensive proposition over time.
McAdam compared the cost of three IBM products, the FastT SATA disk system, a tape library and the DR450 disk-based appliance with tape on the back end. She made the following assumptions:
- Initial storage requirements -- 50 TB
- Annual growth rate -- 10%
- Average tape utilization -- 85%
- Average compression 2:1
- Average disk utilization -- 70%
- No data expiration during the first 7 years
Including electrical power and square footage charges, the disk system cost $1.18 million over 7 years, while the tape library cost $200,000 over the same period. Maintenance costs, the cost of replacing disk or tape, software prices and the cost of phasing in equipment purchases were not factored in to this hypothetical scenario.
"The disk systems cost more up front, continue to cost more over the years, and do not last as long as tape," McAdam said. "Go figure." She will be presenting this study in detail at the Storage Decisions show in Chicago later this month.
Despite the obstacles, disk-to-disk backup is gaining traction, and the venture capitalists, at least, still believe it has legs. Copan Systems Inc. just won $25 million in Series B funding for its Revolution 200-T high-density disk device that aims to replace tape libraries for data backup and archiving.
Other disk-to-disk backup vendors out there include: Avamar Technologies Inc., EMC Corp., Network Appliance Inc., Nexsan Technologies Inc., Quantum Corp. and StorageTek Corp.