Those of us looking into a cheaper alternative for centralized storage system should be looking into two open source solutions that can turn any old PCs into a functional network attached storage (NAS) as well as storage area network (SAN) devices. As of this writing, both of these solutions are free to download and use with Openfiler giving support and documentation at additional cost to the user.
I am running Openfiler as a SAN in my VMWare virtualization lab. It can be installed on a bare PC or can also be installed on virtual server.
For comparison of the two solutions, i am posting the following websites which have a fair comparison of the two solutions.
http://blog.patyuen.com/lessons/technology/openfiler-vs-freenas-tips-for-building-your-own-nas/
http://www.linuxbsdos.com/2008/10/06/freenas-vs-openfiler/
Securing What Matters 