Sidebar: Continuous Data Protection: Good to the Last Byte

Computerworld - Take TiVo and apply it to a server backup environment, and you've got an approximation of continuous data protection (CDP), or time-addressable storage.

CDP technology saves all application changes as they are happening at the bit level, time-stamps them and moves them off to disk to be stored. If a data restore is required, a systems administrator can literally dial back an application to any point in time, even seconds before a virus struck a server. That contrasts with synthetic backups, in which a rules-based engine determines how often data snapshots or incremental data copies are taken to capture changes made to files or volumes.

"The big benefit of [CDP] is you're never caught between 4:07 p.m. and 4:10 p.m. saying, 'I wish I had data from 4:08,' " says Mike Kahn, an analyst at The Clipper Group.

Harold Weiss, a systems engineer at Memphis-based Baptist Memorial Health Care Corp., which runs 15 hospitals in three states, has been testing Revivio Inc.'s CPS 1200 CDP product. He rolled it out in February and plans to put it into production in May. Weiss has more than 660 Wintel servers and 30 HP-UX servers, along with 96TB of storage on a SAN that he expects to grow to 158TB by April. Weiss initially installed the Revivio CPS 1200 to protect financial data contained in a database from Lawson Software Inc.

"We've been able to recover in our test environment the loss of a system in 15 minutes from the time we caused the database to corrupt itself," he says. "If we were doing that without these [CDP] products, we'd have to do a complete restore. That's taken us eight hours."

Weiss is so enthusiastic about the technology that he plans to use CDP to back up all patient records, including radiological images and other sensitive patient information.

"When you create your data sets, those can reside across different servers and still be part of a single data set inside this continuous protection system," he says. "So if I have to go do a restore, I can go and restore all those systems to the same point in time."

There are two conceptual differences between straight synthetic backup and continuous data protection: Synthetic backups require sysadmins to choose how often and at what points in time they want to perform incremental backups. CDP schemas create logs of any file or volume that has changed and then provide an instant restore from any point in time when queried to do so.

However, there are as yet no products for building up incremental backups for a full synthetic backup or restore.