* The Reviewmeister takes a look at NSI Double-Take For Windows
Continuing our quest for products that kick in when your Exchange server kicks out, let’s look at Double-Take for Windows.
This is a byte-level replication system. Sources of datasets (drives, volumes and folders) are identified. Then target storage areas are calculated for size and subsequently allocated for replication. In many installations, one target might suit several data sources, but for Exchange, NSI recommends a one-to-one allocation if the targets are going to be used for subsequent/possible failover.
The first step in the process is replicating the database. The mirroring took 530 minutes to replicate our datasets, consisting of Exchange executables and Exchange stores for both of our two primary site servers.
This initial synchronization was simple to set up and deploy, but additional steps such as batch file configuration and finding Exchange files, for example, are required.
In our two-forest, two-Exchange server example in which we simulated a headquarters and a manufacturing branch topology, four licenses of Double-Take were required, but only two licenses of Exchange server were required.
When failover occurs – as detected by a failure threshold that can be set for communication between servers – the software triggers options you set in a recommended batch file that calls NSI’s ExchFailover command. This command starts Exchange on the failover hardware and sets DNS information to the target server.
The real test was to find out whether vendors’ implementations could sense the primary site was down, then recast the hotsite’s mirror to Exchange users. After the power failure we assessed how products detected the outage. We then wanted to see the products bring Exchange services back online by using our VPN connection to fail over operations to the secondary site. We tracked how many messages were lost during failover and clocked time to availability. Double-Take for Windows does this automatically.
For the full report, go to https://www.nwfusion.com/reviews/2004/0503rev.html
