I’ve used Starwind only in a test environment running on a single box (HP Server). I would not feel comfortable running production servers with this software-based iSCSI San. HP LeftHand Networks is another software-based iSCSI San that runs on standard x86 hardware but it does provide the redudancy and scalability you would want in a “san” solution. I prefer hardware-based properiery hardware for the fact of performance and integration to major components like Exchange, VMware, SQL, Oracle, etc.
Starwind does support thin provisioning in the newest version, as well as data replication so that you can have a highly available solution using block level replication between two seperate storage servers.