Productive Corporation

• Continuous, asynchronous, byte-level replication:
  Double-Take monitors changes to all protected files and replicated only the actual bytes that change.
• Unlimited distance replication:
  Replicate to a disaster recovery site as far away from your production server as you would like, over standard IP networks, for maximum protection against data loss from regional crises and other disasters.
• Hardware independent:
  Double-Take allows the flexibility to choose best-of-breed hardware and software as your enterprise grows.
• Flexible Bandwidth Scheduling:
  Limit network use of Double-Take during busy work hours and increase or remove these limits during nonpeak times for very efficient replication with the least amount of impact on production resources.
• Use standard network protocols:
  Replicate over any existing IP network, LAN, WAN, VPN or NAT so you can deploy without additional infrastructure costs. 

There are different Double-Take licenses depending on the operating system you are using.  Be sure you have the correct license for your operating system. 

a. The Small Business Server Edition license is a replication only license, unless you are using Full-Server Failover
b. There are two SSE (Storage Server Edition) licenses which run on the same operating systems.  The SSE license contains full functionality while the Replication SSE license is limited to replication only.  There is no failover functionality available with the Replication SSE license. 
c. The Itanium Edition does not support Full-Server Failover