Protecting your data against human mistakes, not device failure

Computerworld - Continuous data protection (CDP) and its close cousin, data snapshot technology (which might be considered "CDP on the cheap"), are the latest fashion among backup/restore vendors.

IBM, for example, is promoting its Tivoli Continuous Data Protection for Files product under the slogan, "When once a day is not enough."

The implication, which some vendors are pushing, is that this is a replacement for other kinds of backup, better than tape but less expensive than the three-node architecture.

CDP/snapshot backup, however, is a new approach aimed at a different problem than traditional backup/restore solutions, says Peter Burris, consultant and co-founder of Wikibon.org. "CDP is a first important attempt at providing protection against both human error and against data corruption caused by unanticipated interactions between applications," he says.

While these issues have caused problems since the start of the computer age, they are becoming more important, Burris argues, as end-user computing moves from desktop and laptop systems to mobile handheld devices. "On a PDA, all it takes is an accidental swipe of a stylus or tap on the wrong tiny virtual button to wipe out an important e-mail or document," Burris says. Simultaneously, the advent of service-oriented architecture (SOA) increases the potential for data corruption, not only from unanticipated interactions among applications, but also among pieces of code inside an SOA application.

Killing mosquitoes with a sledgehammer

Traditional backup/restore approaches are focused on protecting against device failures ranging from a hard drive crash up to the loss of an entire data center in a regional disaster. Going to backup tapes to try to recover a spreadsheet someone accidentally deleted is like killing mosquitoes with a sledgehammer.

CDP works on a more granular level, focusing on individual applications or files down to the end-user device level. Thus, a CDP system may back up the Exchange database on a specific user's PC. If a user accidentally deletes a critical file, that specific database can be restored quickly and comparatively easily to the state just before the deletion without involving anyone else. The danger of this is that it can create discrepancies between the restored database and the rest of the system, so, for example, e-mails that arrived after an incident may be lost from the user's Exchange database. These, however, can be restored from the server.

This, however, is exactly why CDP/snapshot shouldn't be considered as a replacement for normal backup technologies such as tape, warns Wikibon co-founder David Floyer. The discrepancies that are easily fixed on one PC or one application become impossible to manage when trying to restore an entire database.