CDP and Backup Software: The Fundamental Differences

Here's a question for you to answer. Backup software and continuous data protection (CDP) software: same or different? And if different, is CDP software a replacement kind of different or a complimentary kind of different? This is a critical question for companies to answer as they contemplate the adoption of CDP software in their enterprise because the answer to it influences how companies spend their money and in what circumstances.

Backup software is an integral part of many companies' core IT operations so the idea of replacing it with CDP software can be a discomforting thought for these individuals within organizations. However a "rip-and-replace" strategy is not necessarily the correct way to view CDP software either. To perceive it correctly, companies should first have a fundamental understanding of how backup and CDP software differ from one another, what specific problems that each one is designed to address and then how to best position these two respective technologies appropriately in your organization.

First, backup software and CDP software are respectively designed to take advantage of technologies that are/were widely available, inexpensive and abundant at the time they came into existence. In the 1990's, tape was much more inexpensive than disk so backup software was designed to take advantage of tape's lower costs as well as to manage tape media. Meanwhile CDP software has came of age in the 2000's as the cost per GB cost of disk has dropped - primarily as a result of the widespread corporate adoption of Serial ATA (SATA) disk drives.

Second, backup software was developed to satisfy lower corporate expectations for recovery that existed in the 1990's. Companies were once content to know that they could only recover data from last night's backup and accepted the fact that they had to make other provisions to recover data that was new or had changed since the backup occurred if they needed a more robust recovery. Today's application owners and users are not so forgiving of that approach anymore. CDP addresses these higher recovery expectations by giving application owners and end-users the option to recover data back to any previous point in time.

Third, CDP is intended to store data on disk for relatively short periods of time while backup software can store backup data on either disk or tape for relatively long periods of time. While companies can configure CDP software to retain data it has protected for any length of time, realistically speaking most recovery requests (~80%) for data occur within 7 days from when the data is protected and almost all requests (~95%) within 30 days of when the data is protected. Hence it makes sense to keep data on disk to expedite recoveries.

However keeping all data on disk forever is not always cost-effective and companies may still have internal or regulatory requirements to keep copies of this data for months and years. In these circumstances, using backup software to move the data from disk to tape is still the logical and best way to tackle this. Not only can backup software copy and/or move the data from disk to tape, but it can also manage the tape libraries and cartridges on which the data is stored.

Further, using CDP software in this situation not only complements backup software, it actually enhances its capabilities. Products like InMage Systems' DR-Scout have the capability to create consistent, point-in-time snapshots of data it protects and then presents these snapshots of the backup software for backup. This provides the backup software with unfettered access to previously backed up data, off-loads the overhead associated with the backup from the application server to the CDP server and expedites the transfer of the data from disk to tape since the backup job is not competing for server resources as frequently occurs on application servers.

So the short answer to the question I posed at the outset is that backup software and CDP software are both complimentary and competitive software packages. On server hosts I would classify them as competitive as CDP software potentially replaces the need for backup software agents. However once the data is centrally protected by the CDP software, backup software compliments CDP software by handling the management and movement of backup data from disk to tape to meet other concerns (such as archiving, regulatory, and retention) that the organization needs to satisfy.