If you are looking for a open source SAN to avoid purchasing expensive hardware, you can actually install open source software to act as SAN.
If you have a iSCSI Server with few TB hard disk, you can install “openfiler” or “freeNAS” to use as SAN. They are the best alternative of using expensive hardware version of SAN.
You can try to see how it works. But openfilter seems working great for people who are using VMware vSphere / ESX Server.
Nice article based on this is here: http://www.windowsnetworking.com/articles_tutorials/Options-creating-software-based-Windows-iSCSI-Server.html
Monir's Blog 