Good Afternoon,
Are most NASs compatible with Solaris/RedHat? Specifically, I'm looking at Western Digital ones but none of them say they are - I like My Cloud Pro Series PR4100
My Cloud Pro Series PR4100 � Network Attached Storage | Western Digital (WD)
You have to look at the network (sharing) protocol(s) that they support.
The link you posted lists support for Windows and Mac but not Unix/Linux ie, NFS protocol.
A NAS with compatibility for Unix/Linux will usually support NFS.
In this context a NAS supporting Samba is Windows compatible.
Call the manufacturer and ask whether the product supports NFS.
Obviously, if you install a Samba client on a Unix/Linux box then you can access Windows shares whether offered by a Windows system or a NAS offering Samba support.
It depends what you want to use it for. If you are looking for general storage that any user can access then you need NFS support.
And, of course, if you have an old machine laying around with enough drive slots you could build your own NAS (and even support RAID within it) using OpenFiler or FreeNAS .