The latest continuous data protection (CDP), or continuous backup, products promise administrators the ability to recover from a point in time--going back minutes, hours, days or even weeks--on a range of platforms. They offer the flexibility of restoring individual logical unit numbers (LUNs), defined volumes or single files.
CDP products differ from point-in-time snapshots in two key ways. First, data changes are recorded continually, as opposed to halting an application's I/O activity to create the data snap. And second, data changes are stored incrementally rather than storing numerous data images. A growing number of products also provide the ability to:
- Recover from any previous point in the past, rather than certain fixed points
- Create a central data store that multiple servers can use for backup and recovery
Because of the differences among CDP product offerings, administrators must sort through them to identify the tradeoffs that each one will present to their environment. Administrators should consider these factors:
- Dual write-performance penalties
- Reliability of the CDP application
- Difficulty of deployment
- Maintenance of the application
- Additional storage requirements
- Impact of the agent on the server's I/O
- The different types of applications that are supported in the environment
CDP applications are either host or network based, and may operate on a block or file basis. Some are implemented as in-band or out-of-band appliances, while others are application aware.
When selecting the right CDP product, administrators need to determine the type of environment the product will be deployed in and where they want to recover the data from. To protect an application with direct-attached storage, administrators should choose host-based CDP software that can take advantage of either locally attached or IP-attached storage. For applications with network-attached storage, they should consider host-based agent products now, but look to storage network-based alternatives as they become more mature and stable.
