Double-Take vs. Steeleye DataKeeper Cluster Edition

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1 Double-Take vs. Steeleye DataKeeper Cluster Edition A Competitive Analysis July 2012 Double- Take from Vision Solutions is compared to Steeleye DataKeeper Cluster Edition. A summary of the performance of each product in important functional areas is presented, as well as an analysis of the likely fit for each technology as Microsoft clustering technology evolves.

2 Double-Take vs. Steeleye DataKeeper Cluster Edition A Competitive Analysis July 2012 Overview Double- Take Availability 6.0 was released on May 1, Double- Take Availability Advanced Edition (required for GeoCluster support) is priced at $4300/server plus annual support of $1100. SIOS offers the DataKeeper Cluster Edition $3000 per server plus annual support of $620. Both products integrate with Windows Server Failover Clustering, extending the Microsoft solutions with shared- nothing clustering and multi- site clustering. An analysis of the effectiveness of each product in providing high- availability and disaster recovery for business- critical information systems is conducted and results included. Installation and Configuration Both systems provide a Windows GUI Installer, yet each system has plenty of caveats regarding upgrades, multi- system installation, etc. A nice feature for both products is the automatic configuration of the Windows Firewall during the install process. Uninstall was effective for both products. Windows Integration Steeleye products integrate well into the Windows architecture. Both Double- Take and DataKeeper products integrate with Performance Monitor, Local and Domain Security, use Microsoft Management Console, integrate with Event Logging, etc. In general they are both natural fits into the Windows ecosystem. Both products have some room for improvement to integrate better with the Windows OS visually and conceptually. Performance Optimization Overview 1

3 Double- Take and DataKeeper offer a comprehensive set of performance counters that are integrated into the Windows Performance Monitor. These enable real- time monitoring of system status and activities as replication, monitoring, and failover occur. User Experience While the GUI interfaces for both products enable the required functionality, the DataKeeper GUI and Windows integration provide the most natural solution for an experienced Windows admin. The DataKeeper GUI is an MMC snap- in providing a familiar Windows interface for configuration and administration. Beyond initial setup, DataKeeper replication functionality is managed and monitored from the standard Windows Failover Cluster Management tool. The Double- Take console GUI is a stand- alone native windows application. Double- Take may also be managed from the Windows Failover Cluster Management tool after installation and initial setup. Both GUIs offer adequate responsiveness and are intuitive. The Double- Take GUI enables viewing and changing more configuration information and provides more details on the state of the replication process, including the sizes of the write queues and percent of data protected at the target during resynchronization (resync) periods. As this GUI will not normally be used while under cluster control, this is of limited value. Both systems make all of this information viewable in Event Logs in more detail. Error logs are well categorized and provide useful information on replication and failover events and status. Double- Take provides Alerting through Microsoft Systems Center Operations Management, including alerts on replication service state, errors, hitting high- water marks, etc. This is useful information presented within the preferred system for monitoring and alerting in Microsoft environments, a plus for Double- Take. Documentation Steeleye documentation for DataKeeper is well organized, complete, and attractively formatted. It is easily available on the web and can easily be found via search engines. Double- Take documentation is also complete, but is very complex. It is likely that the complexity of the documentation is reflecting the additional protection modes but appears to also reflect the underlying complexity of the product itself. The Double- Take Availability Users Guide is more than 850 pages! User Experience 2

4 Data Replication Efficacy Double- Take vs. Steeleye DataKeeper Cluster Edition At the core of an effective high- availability solution lies the requirement to insure that multiple copies of the data are available in the even that data is lost, corrupted, or becomes unavailable at its normal operating location. Steeleye DataKeeper and Vision Solution s Double- Take are both designed to replicate data, either within the datacenter, within a metro- area network, or between a datacenter and a remote location. Replication CPU Overhead In head- to- head tests, Steeleye DataKeeper repeatedly demonstrates a very high level of efficiency in replicating data. The DataKeeper replication engine consistently operates as a low overhead task on the Windows server, consuming only a few percent of the CPU during the replication process. In all cases tested, DataKeeper consumed a nearly immeasurable amount of CPU cycles on the test server. Even under stress tests inserting 1,000,000 rows of complex data into a database, DataKeeper processes and services consumed 20 times less CPU cycles than SQL Server. Double- Take, on the other hand, was consuming at least two times the CPU of SQL Server even with compression disabled. In all tests runs, Double- Take was by far the largest single consumer of CPU time. Perhaps for this reason, compression is turned off in the default installation configuration for Double- Take. Turning off compression offers little relief but consumes nearly twice the bandwidth in tests. In addition, adding additional hardware failure points to a WAN link is not advisable if the goal is higher availability. In all aspects, including memory, CPU, and WAN traffic, Double- Take proved in lab tests to be dramatically inefficient compared to DataKeeper. IT professionals considering Double- Take should prepare to spend more on server CPU and memory hardware, datacenter space, and communications bandwidth. Replication Performance and WAN Traffic In a case study performed for this analysis, a database was designed with three columns. The first column and primary key was a generated UUID. The second column was a short text field. The third column was a large randomly generated text field of fixed length. 1,000,000 rows were generated and inserted into the SQL database while the database files were being replicated using DataKeeper and Double- Take Availability 6.0. Results for the insert are as follows: Product Elapsed Job Time on Source Rows Inserted Replication CPU Usage Steeleye 11:21 1,000,000 < 1% - background level Double- Take 14:21 1,000,000 4 times SQL Server (9%) Data Replication Efficacy 3

5 It should be noted that Steeleye DataKeeper CPU usage was not visible on the list of top 5 CPU users during the job. Double- Take, however, was consistently the top CPU user, frequently using 4 times or more the CPU of SQL Server processes. After performing the insert exercise, another exercise was performed involving database updates. 100,000 rows in the database table were selected randomly for updates. The update exercise was executed on each product yielding results as follows: Product Elapsed Job Time on Source Table Rows Updated Replication CPU Usage Steeleye 1:23 100,000 < 1% - background level Double- Take 1:54 100,000 5 times SQL Server (12%) Bytes Sent Note that the DataKeeper product resulted in faster job completion on the source server, much less CPU overhead, and significantly less bytes transmitted to the target, resulting in lower bandwidth utilization. Both products were set to use medium compression. Double- Take uses Byte- Level replication and as such claims to be more efficient that block- based replication technology like that employed in DataKeeper. Real world applications, however, do not write or update data a byte, or even a few bytes, at a time. In fact, due to standard TCP packet networking overhead, if applications did frequently write in smaller chunks the Double- Take technology would be even more wasteful and inefficient. With IPv6, the header overhead for TCP transmissions is twice as high. Logic backs the experimental results byte level replication is a disadvantage from a replication performance standpoint. DataKeeper is efficient in WAN utilization and does not require the addition of WAN accelerator hardware. Double- Take may require WAN accelerator hardware on both ends of a link to avoid CPU overhead and to more effectively utilize the WAN link. These accelerators are themselves potentially single points of failure that can result in overall geocluster/dr failure. Data Integrity and Recovery DataKeeper provides synchronous as well as asynchronous replication, enabling near zero data loss and continuous data protection. Double- Take offers asynchronous replication only and supports disk- based queuing of writes, resulting in the possibility of significant data loss on failure of the source server while a large number of writes Data Integrity and Recovery 4

6 are outstanding and not yet mirrored. In test cases with inserts and updates on a one million row database, several gigabytes of data were held in the write queues and subject to data loss a potentially catastrophic event. DataKeeper enters a partial resync mode combining multiple writes by sending updated block data, reducing the amount of data to be transmitted and resulting in a more updated mirror, achieving a better Recovery Point Objective (RPO) in case of a failure. Conclusion While Double- Take and DataKeeper Cluster Edition offer similar functionality, there are some clear differences. Double- Take, after being acquired by Vision, is now but one technology in a portfolio of software technologies in the new company. The focus of the larger company appears to be on delivering a broad multifunctional suite of utilities for backing up, moving and replicating virtual machines. Most of these offers involve moving data around the enterprise in the normal course of systems management. The critical nature of high- availability and disaster recovery no longer seems to be the main focus of the company. DataKeeper Cluster Edition provides several key advantages over Eliminates need for WAN accelerator hardware through more efficient WAN utilization Significantly lower memory and CPU usage during replication Higher data integrity option with Synchronous mode Better attainment of Recovery Point Objectives by less data in transit to mirror More natural integration into Windows server management interfaces DataKeeper is $3700/server less expensive than Double- Take over 5 years SIOS s DataKeeper Cluster Edition proves its superiority in data replication and integrates seamlessly into Windows, making it the better choice. Conclusion 5

7 Comparison of Double- Take Availability and DataKeeper Cluster Edition Pricing and TCO Installation and Configuration Windows Integration Performance Optimization User Experience Documentation Data Replication Efficacy Data Integrity and Recovery Double- Take Availability DataKeeper Cluster Edition Conclusion 6

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