Energy efficient, low-heat closet-server?

Question

I'm currently using a Ye Olde HP Compaq nc6220 running Ubuntu Server 15.04 as a server to run odd jobs in my closet. It's doing fine, but the room can get a little toasty (which is fine) and I'm fairly certain it's not the most energy efficient setup.

Some examples of the odd jobs I run on it:

• Downloading the SE data dump about twice a year to a big external hard drive (it's around a 30GB dump) over a torrent
• Playing music through a 3.5mm headphone jack throughout the day, managed by a cron job
• Running a very, very low volume Apache server (it's on my local network, so this is basically no load beyond the base Apache-running load)
• Running low-volume Rails apps
• Testing whatever else I want

Since it's running Ubuntu Server, I can run almost anything on it. The issue I'm running into is running things that require a 64-bit architecture - the nc6220 is 32 bit.

So, I need something that:

• Is fairly cheap (less than it would cost to run an Amazon EC2 server for a couple years, meaning < $200ish, but I'm flexible on the price
• Has a 3.5mm headphone jack, or a way to output audio to that in some way (I don't care about it having a speaker)
• Has a USB port or two, for connecting that external data dump hard drive
• Has an Ethernet port or WiFi
• Can run a capable version of Linux - defined as being able to run Rails apps and compile C programs.
• Won't suffocate or melt in a room with terrible ventilation (think about thirty square feet and no airflow)

I'm less concerned about 64-bit compatibility, but it would certainly be a plus. What would work for this?

Answer 1

With these fairly low requirements, any of the mid-range ARM boards would fit, so you might as well go for a Raspberry Pi by default. (Model 2, the earlier models aren't worth the slightly lower price.) The reference price for just the board is $35, plus a power supply gets you

• 4 USB2 ports (keyboard, mouse, external drive, 1 spare or wifi)
• 100 MB Ethernet — on the USB bus, so not ideal for heavy duty storage server, but ok for downloading stuff over a typical home Internet connection.
• Jack and HDMI audio output.
• Lower power consumption than the external hard disk.

The CPU is not nearly as fast as the latest Intel offering, obviously, but it's enough to run ordinary Ruby programs and do C compilations. (I wouldn't do big C++ or Java compilations though, but more than the CPU, the limiting factor is that there's only 1 GB of RAM).

Since this is well under budget, you might consider a higher-end ARM board. 64-bit ARM boards (ARMv8) within your budget are starting to appear. (Of course, that's if you want 64-bit for some reason, not if you specifically need x86_64.) There's at least HiKey board is attempting to be a reference 64-bit board. It has a 1.2 GHz Cortex-A53, built-in USB2 and wifi, HDMI, 4 GB of onboard flash memory. There's also the cheaper Dragonboard 410C, with 8 GB of onboard flash, 4 USB ports and wifi. Unfortunately both have only 1 GB of RAM, at which point there are few benefits 64-bit CPU (there can still be benefits from other architectural improvements such as extra registers and cryptographic accelerators). I can't seem to find an affordable 64-bit board with 2 GB or 4 GB of RAM. You may want to start out with a 32-bit, 1 GB board now and use the rest of the price for a 64-bit board in a year or so if you find the need.