CDP Versus Snapshots; It's About Recovering the Business, not the Application

In recent weeks, questions about what advantages does continuous data protection (CDP) technology like InMage Systems' Scout have over snapshots has come up more than once. Prompting this debate is whether companies can achieve the same type of near real-time recoveries for mission critical applications using multiple snapshots, or near-CDP, as they can with CDP if snapshots are used in conjunction with database transaction logs for application recovery.

The major difference between snapshots and CDP is that snapshots do not capture all application write I/Os like CDP. The reason that some argue that snapshots are as good as CDP is that companies can still achieve a point-in-time recovery when using snapshots in conjunction with database transaction logs. When doing a recovery, companies can select a specific snapshot and then replay the database's transaction logs from that point forward. This creates a point-in-time recovery similar to what CDP can deliver.

Despite this similarity, CDP provides three fundamental advantages over using a combination of snapshots and database transaction logs for recovery.

• CDP simplifies the recovery process by reducing the complexity and time needed to perform the recovery. Using snapshots and database transaction logs, companies typically need to involve both the backup administrator and the database administrator to recover the data. The backup administrator recovers the snapshot while the database administrator (DBA) loads and replays the database transactions logs from the time that snapshot is taken. All of this is coordinated in order to complete a recovery equal to CDP. CDP streamlines the recovery process by enabling IT staff to perform the entire application recovery from a single CDP product. Using this method, the backup administrator can recover all of the data needed to recover the application without creating a dependency on the DBA being present and replaying some of the database transaction logs.
• One central CDP product creates a consistent, repeatable pattern for application recovery. Using snapshots and database transaction logs, there is no consistency in how recoveries are performed. Recoveries become a process of trial and error as specific snapshots are selected and administrators identify the specific database transaction logs needed to recover the application. Using CDP, companies have one central interface they can use to recover applications across the enterprise. This helps to eliminate dependencies on specific applications and IT staff.
• CDP supports the recovery of multiple applications to different points in time. Corporate application servers typically have dependencies on one another such that data generated by one is used by another. The problem that emerges is that data corruption in one application can impact other applications. There is no one point that companies can identify as a recovery point for interdependent applications. Using CDP, companies can recover each application back to a specific point-in-time just prior to when the corruption occurred on each specific application server rather than trying to take all of the applications back to one point in time.

The major differentiators between snapshots and CDP are the ease of use and the scope of application recovery that they can provide. Snapshots will always introduce dependencies on database-specific transaction logs and specific people to deliver, at best, an application-specific recovery that is more complex to setup and manage. Conversely, a CDP product like InMage Systems' Scout is designed to centralize, simplify and expedite application recoveries to multiple points-in-time. It can manage interdependent applications and eliminate undesirable dependencies on specific products or people. However, on a larger scale, CDP gives companies a higher degree of assurance that they can recover not just a specific application but the entire business back to a known, good point-in-time.