How much memory does a storage node need?
Right now, the Installation Rquirements at
http://www.foss-cloud.org/en/index.php/Installation_Requirements
state 8GB of RAM as the lower limit of memory.
Does a storage node really need that much?
The installer has a hard limit of minimal 4GB.
But physically having 4GB RAM does not fulfill that requrement ... I think it measures free memory and the installer comsumes some himself.
I'm able to install storage nodes with 4GB physical RAM if I set the limit to 3.3GB in the installer.
So, if my assumption is correct and a storage node is fine with 4GB (or less) RAM - then I would suggest setting the limit in the installer to 3.3GB for storage nodes.