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FilesX offers the same recovery capabilities for file system data as well. In addition, it offers an interesting capability for system-level recovery. A significant problem in disaster recovery scenarios is bare metal restore. Maintaining system images that are current with security patches, drivers, application changes, etc., is an enormous effort. With FilesX, system disks can be regularly snapshot along with other file systems. To recover, boot from a CD, connect to the FilesX repository and re-paint your system disk as it appeared at the point of the last snapshot.

XOsoft Inc. XOsoft's Data Rewinder is another example of a software-based continuous backup product. At the core of Data Rewinder is a filtering file system layer, known as XOFS, that sits directly above the standard OS file system in the data stack. All file system writes pass through XOFS. As data passes through to the file system and to primary storage, Data Rewinder simultaneously creates a "counter event," which is essentially an "undo" command that's sequentially written to a journal, presumably located on separate storage volumes.

If data corruption occurs, an administrator can view the journal and select a point in time to "rewind" the data. This is accomplished by sequentially executing the undo operations to return the data to its exact state at that point in time. The time to perform these operations will vary, depending on how far back in time you need to

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go, but it will be much quicker than restoring an entire image from a backup.

Unlike the other products discussed here, Data Rewinder resides on the host system it's protecting. This is because much of the functionality in Data Rewinder is derived from XOsoft's data replication product, WANsync, and the products are intended to complement one another. One of the key features of the product is support for specific applications, including Exchange, SQL Server and Oracle. Also, Data Rewinder restores the original volume to a specific point in time, so the product can't be used to restore individual files or e-mail messages.

Mendocino Software. Mendocino is one of the newest and one of the oldest entrants into the continuous data protection arena. Mendocino acquired the technology assets of Vyant, including their CDP software product RealTime, which has been shipping since early last year. RealTime is architected for an application host server to be paired with a dedicated backup server, making it most appropriate for environments where a fixed number of selected servers require CDP-class protection.

On the host side, an Intercept Agent continuously captures write operations on a server to a serial buffer, and then transmits them asynchronously via TCP/IP to the backup server. On the backup server, a backup agent maintains a "nearly current" replica of the primary storage while an archive agent maintains forward and reverse incremental journals that enable quick movement forward and back through time to view and access data. This is accomplished via a "time slider" interface that can quickly present virtual volumes at any point in time based on the capacity of the backup server.

If data loss or corruption occurs, an administrator can slide to any desired point in time and mount a virtual image. A copy of the production application would be run on the backup server, and testing would determine if the corruption was still present. This can be repeated until the optimal point is determined, then the image can then be committed to primary storage via a restore agent. Virtual images can also be used for other purposes such as nightly backups and problem analysis.

This was first published in June 2004

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