Dilemma Gigantica

Oké. At the moment I run a server at home. This server runs several services which I need (at the moment). These services include:

• File sharing
• Web server (mostly for testing and development, since this website is hosted @ Dreamhost.com SquareSpace.com)
• *cough*Download station*cough*
• Mail Server (serving several personal domains)
• SSH Server
• Local onsite backups

All this runs on an old (especially in IT terms) PC with Windows. The CPU and other peripherals sucks in electricity like you've never seen before (it's an old AMD Thunderbird CPU from the early overclocking days -> 2000/2001). Apart from being old, it's also responsible for about 70% of my energy bill (a 'rough' estimation). Besides that, it's also responsible for permanent subtropic temperatures in my study.

Trying to be a bit more 'green' I want to replace the old piece of metal with something a bit more energy efficient. And this is where the Dilemma Gigantica comes in; What to get to replace the old 'faithful'?

My choices are an Apple Mac Mini with an additional 1TB external drive OR a Shuttle barebone PC with 1.5TB. The Apple configuration is a bit more expensive, but is extremely silent and uses like no energy.

Picking the Apple would result in figuring out the mail server part (which I might transfer to Dreamhost in the near future), getting Adobe Coldfusion to run on OSX, but would also result in a 100% Apple environment (if you don't count my Popcorn Hour). The Shuttle creates an opportunity to keep my Microsoft/Windows knowledge on a certain level, as well in a relatively easy migration to the new hardware.

So do I want to go for safe and relatively cheap, or go for a challenge which is a bit more expensive (with a quicker return on investment by an even lower energybill)? Either way, the solution will pay for itself.

Anyone has the reason why I should pick one or the other?