This is one for the serious business with a need for high availability and disaster recovery in its overall plan. The capability not only to replicate files but also only the part that has changed, is just one of Double-Take's virtues.
This solution also provides failover, and where the data is critical and must be available at all times that benefit cannot be ignored. However, in order to get the most from this feature, machines being utilized for this purpose should have identical operating systems, configuration settings and applications in place. This will enable the operation to be smooth and trouble free in practice.
Other beneficial resources include mirroring of data. This initially includes the file attributes, so on replication only the changed portion needs to be copied. The method is a fast and efficient use of resources and is accomplished in real time, ensuring all backup data is up to the minute in case of disaster. Many of the other solutions do not offer this real-time benefit, and where data is crucial this method would seem to be the obvious choice.
Installation is simple enough. It takes a bit longer than some solutions, but configuration of target machines, especially in the realm of failover, requires forethought. Then again, all disaster recovery plans should ideally be calculated to extreme limits.
By and large this solution proved the most efficient with the data that we were backing up, and enabled files to be pulled at any time with up-to-the-minute changes still intact. You will need 26Mb for the program to run efficiently, 256Mb for the Double-Take page file, 30Mb for the Windows installer files and 312Mb of free disk space to accommodate the full application, and a minimum 64Mb of RAM.
Double-Take runs on Windows 2000 Professional, Server, Advanced Server or Datacenter; Windows NT 4.0, Server, Workstation, Enterprise Edition or Terminal Server Edition, with SP 4 or higher, and requires TCP/IP protocols. If you intend replicating large quantities of data you will need the space so allowances should be made for that.
Overall Double-Take provides a very useful and complete disaster recovery solution, which enables the enterprise to tailor a plan directly to its individual needs.