Well I started with CentOS and as that could not handle the new advanced format drives it was a nightmare. Then finding the WD Greens were really no good in a Raid 5 array (or any array by reports on the internet) added more hardship. Problems sourcing the right hardware for the server so I could connect all 20 bays and a few false starts also didn't help but it is all more or less sorted now.
Fedora 14 was easy enough. Straight install and then just setup samba via the GUI and sort out Selinux tagging or it will disable all access to the shares after it detects a possible intrusion..... That is really a bit of a pain but once you have tagged a drive correctly it is fine.
I chose Linux as I can script backups and a few other things although it is still pretty manual at the moment. I will also move on to NFS when I can get a client for the Win7 PC.
The Fedora server is running as good as gold though. Give or take the SeLinux security 'features' I have had no issues and even use FreeNX to remote desktop to it from Windows or use a telnet app from my phone if need be.
The big plus for me though is that if the OS dies / gets corrupted etc, I can just transport the drives into another machine running Fedora / Redhat and possibly even Debian (Unbuntu etc) and the drives should work without any data loss inc the raid array.
Having had problems with tagging drives in Windows and not being able to easily move them from machine to machine I have steered clear although it seems lots like the drive pool in WHS

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Oh my job is working on Solaris boxes so Linux is a pretty obvious choice for me.
RB