I have searchstorage.co.uk send me potentially interesting white-papers regularly. If I am honest, most of them or thinly veiled press-releases. However occasionally one is interesting.
Today I received one entitled Break free of vendor lock-in with open source storage. Being a FLOSS fan and a storage specialist, that obviously intrigued me.
The article of interest starts on page 8 and is pretty good. It mentions all the main players; unusually it is not condescending towards Open Source (i.e. it will get you by until you can afford to buy a proper/stupidly-over-priced solution).
It also mentions GlusterFS, which is particularly interesting. I have just built a solution at work built around this and it excellent. I will be putting more info up soon as a complete how-to on building a full-featured, high availability SAN/NAS.