We use XOSoft at the company I currently work for. It's quite good at failover, and horrible at failback.

If we want to start using the DR servers, it's very fast. If we need to move back to using our regular servers, XOSoft takes over 24 hours to recover back to them, and ties up both sets of servers and all available bandwidth in our network while doing so.

With SQL failover using XOSoft, it can have problems with the mdf and ldf files ending up out of synch with each other, since it operates on blocks on the hard drive. If a transaction is interrupted by a drive failure, the blocks that have been copied to the DR site can be out of synch, making the database unrecoverable. This is rarely a problem, but we have seen it once (which is too often), in one test.

We're in the process of moving to SQL native DR at this time, because of these factors.

(Note that XOSoft was a considerable improvement over prior DR plans/methods for this company, when they didn't have a DBA and were going from "no DR" to "any DR". It's just that we can do better now.)