I hope I'm not opening too big a can of worms by asking this question...

I'm setting up a new machine (dual Opterons, 2 GB Ram, 4x 400GB SATA disks in software Raid-5) primarily as a file server, but also want it to double as a workstation on occasion. I want a full 64-bit system with a 64-bit kernel and 64-bit applications.

For this application, which is "better", Fedora, or Ubuntu?

WHAHAHA????

a 2 way opteron server and you seriously want to choose between 1) a beta os for linux developers 2) a desktop os for newbies? are you mad? use a proper server operating system, like rhel, sles or centos.

I don't need or want a "server" OS. This isn't for a production environment or even a small group environment. The file server is simply a large raid array where I store MP3 files and digital pictures on my small home network.

acid_kewpie, keep in mind that in Linux world there is no such a big difference between a "Server OS" and a "Desktop for newbies" like there is between MS Windows Server 2003 and Windows XP Home. The server consists of services and applications combined with a specific kind of kernel and hardware, and such a box can be created out of almost any Linux distribution. I wouldn't say either that Fedora is a beta os for developers nor that Ubuntu would be a "newbie desktop os", since that's just not true. I've seen both "in action" and can say that they will make a server if you just wish. It's a weakness of mind and imagination if you're saying you need RHEL for a good server.

I myself make mistakes every day calling distributions "Linux"; actually the only thing that's "Linux" is the original kernel sources. And those sources can quite easily be recompiled by anyone to his/her needs. The rest of the distribution is just something else, software, ideas, wishes, and they can too be altered as much as you like. Thus you cannot say you need a "specific Linux" if you want a "real server OS".

fedora is most definitely a development operating system. it's very existing is due to the desire to have a test bed for redhat enterprise. it's messed around with something rotten, and serves a very good function, but it is never suposed to be a product operating system.

I've used all Fedora versions for a dozen servers and they are rock solid. The Fedora always leads the pack. It's robust, easy to use and comes with the latest programs. I think Fedora has made many other distros better because they are always trying to catch up to it - think about it. To me the only difference between Fedora and RHEL is the guarantee backing and support. Also it takes time for developers to learn the new apps, hence, the time it takes for RHEL to integrate Fedora updates - a brilliant way to cover your ass... My second favorite now is Ubuntu.

Reliability trumps all in the server room. I like having a bleeding edge desktop though.

you're missing the point mate, it's not about your experiences or anything, the point is that fedora is a playground for redhat, and you should not use it for a stable environment. i use it at home on my desktop, but i'd never dream of putting on one of my servers at work.