Running a Server at Freezing Temperatures
As a part of a backup solution, I'm thinking of running a backup server in my unheated, unattached garage [...] the temperatures very often drop below zero degrees Celsius.
Notice: this text is a mix of several authors plus personnal updates, I thank everyone
Lubricants become more viscous at low temps:
if it got really cold, the lubricants in the drive spindle could actually become solid, freezing the bearings and burning out the motor.
Tell your PC to never turn off hard disks, never turn off fans. (might freeze if they stop, and not start again).
Thermal expansion of the platters:
Hard drive platters go through a normal amount of expansion because solids expand when heated and contract when cooled. Drive controllers are designed to recalibrate occasionally to check for expansion, to insure the heads are positioned correctly, off-track positioning leads to errors. But I seriously doubt the calibration would work outside the range of temps designed into the controller.
Make sure your case is hardened. Every little critter, including mice, will want to live in the warm case. We had a computer in an astronomical observatory dome and mice built their nest on the CPU. The acid in urine from the mice destroyed the motherboard.
Get a case with a thermostatically-controlled main fan (not CPU fan, main fan). Put this in a 5-sided wooden box (hardened against critters, screened on the bottom) and insulate it with construction foam (inside) on four sides and the top. Half-inch foam will probably do. Vent the system fan out the bottom.
What this will do is create a "bubble" of warm air inside the box that is vented when the fan is running and stable when it is off. This will keep your box temperature roughly even. If you are concerned about cold-starting hard disks after a period of off-time, make sure you have a power supply which remains off after a power loss and add a 100 W light bulb inside the box. When you want to power the system back on, switch the bulb on and leave it for an hour or two before you hit the power button, then turn the bulb off again. Do not bring cold hardware into a warm, humid house to warm up - you will get condensation.
Take the floppy out of the machine, and replace the hole in the front with a blank panel. It might be a good idea to do that with the CD/DVD drives as well. Make sure that the back of the case is all sealed up, (ie, no open holes for old PCI devices you no longer have). Lastly, Don't put anything over or close to it. Your going to need it to be able to suck in air, and evacuate the air with the fans.
Some positive feedback for running such a server at 5C without any problem.
Mind the capacitors min temp specs.