You can download Openfiler from www.openfiler.com.
Openfiler failed to install on my test machines. Ubuntu installs on the same machines. For my requirements, it is quicker to install and customise Ubuntu than it is to try and fix Openfiler.
You can buy support for Openfiler from their site. You can also buy the software preloaded onto a SATA disk at a ridiculous price, most of which is included support.
Built on rPath
Openfiler is based on the rPath distribution of Linux using an rPath utility to generate the Openfile distribution. The rPath system appears to be out of date for hardware support. The two big base distributions of Linux are Debian and RedHat. Ubuntu is based on Debian and is usually more up to date. Fedora is the RedHat based equivalent to Ubuntu. Either Ubuntu or Fedora would be better choices that whatever rPath provides.
Hardware for NAS
When you build a NAS device, there is a strong incentive to recycle old hardware. You probably replace your desktop workstation every year or two with something more powerful. If you work for a company, they will replace based on a three year or a five year cycle. Openfiler does not work with the one and two year old computers I used for testing.
A three year old computer might work because that is usually the time frame to get Debian and other slow Linux distributions to support modern hardware. High efficiency power supplies and processors were available three years ago in the better computers.
A five year old computer is too slow and inefficient. You want a NAS running all the time. To keep the electricity bills down, you want a high efficiency power supply, processor, and disks, all of which were rare five years ago. Consider older computers only for backups that are switched on for a limited time each day.
Openfiler could be useful for building a NAS from a computer that is years old. I do not have a machine old enough to make it work.