Feature

Second-generation CDP

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Application consistency
Unlike files, which can be restored to any of the available recovery points, applications like Exchange and SQL Server require recovery points at which an application was consistent. In case a CDP product detects application-consistent events, it inserts so-called markers into the recovery journal, which are then used during the recovery process to determine and present application-consistent recovery points.

Vendors have taken two approaches to ensure application consistency. The first approach looks at the data stream to detect events at which an app is consistent. "We track events like file-save operations, or Exchange and SQL Server start or shutdown events to determine consistent states and mark these events within the change journal," explains Bob Roudebush, Double-Take Software's director of solutions engineering. Heuristic consistency appears to be favored by products with file-level filter drivers, mostly because the file system provides the information required to determine consistent application states.

Fabric-based and volume filter driver-based products favor proactive consistency in which the CDP product proactively puts the application into a consistent state through application APIs. "We call local backup APIs, such as Volume Shadow Copy [VSS] in the case of Exchange Server, and insert a bookmark in the recovery journal,"

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explains Atluri. Contrary to proactive consistency, the heuristic consistency approach has room for errors.


Vendor assessment
Although many of the original CDP vendors have vanished, their technologies live on in other data protection products. CDP isn't a free option or feature. While the majority of backup vendors charge by the number of protected machines, a combination of a base price and capacity-based pricing seems to prevail for fabric-based and volume filter driver-based products.

EMC and Symantec added CDP to their data protection suites through acquisitions. EMC acquired Kashya to complement its Invista fabric-based storage virtualization product. Symantec has spent the last few years integrating its Revivio acquisition into NetBackup and recently rolled it out as Veritas NetBackup RealTime Protection. Both products compete at the high end of the CDP market, capturing changes at the FC I/O level, and offer broad application support.

IBM Corp. recently extended its Tivoli Storage Manager (TSM) suite with TSM FastBack through technology it acquired from FilesX. Remote-office data protection of Window servers and applications is FastBack's primary target market.

CA entered the CDP market through its XOsoft acquisition, and offers the XOsoft product as CA XOsoft High Availability. Unlike some of the other backup software vendors, CA hasn't yet tightly integrated XOsoft with its backup app and continues to target the SMB DR market where XOsoft has done well.

Asempra and InMage Systems are among the few CDP firms that have survived on their own. Asempra Business Continuity Server and InMage DR-Scout are available from resellers and through OEM relationships. While BakBone Software and Hitachi Data Systems use the Asempra product, Pillar Data Systems and Xiotech Corp. partner with InMage Systems.

Double-Take Software and SonicWall Inc. got into CDP via acquisitions. Double-Take added CDP pioneer TimeSpring to complement its continuous replication software; SonicWall bought Lasso Logic to offer data protection appliances for SMBs with limited IT resources.

Despite its ominous start, CDP has been incorporated into data protection products and its role is likely to expand. Rapid data growth, highly distributed firms with branch offices lacking IT resources, the need for better RTOs and RPOs, shrinking backup windows and the need for 24/7 app availability are all trends that support the increased adoption of CDP.


This was first published in October 2008

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