Should servers be turned off at night?
Solution 1:
To liken it to a car analogy: A taxi can do over 500,000 kilometers before it needs an engine rebuild. The reason for this is because they are always running, 24/7, and after a car's engine is up to temperature, the amount of wear it receives while it is running is greatly reduced.
A computer is kinda the same. The majority of the "wear" on parts can happen when the server is booting up. Just attach an amp meter to your computer, and turn it on. When it starts up, the power it draws climbs very high, and then it settles down once all the disks have spun up and the processor is initalised. Also, think about how much disk activity the server undergoes during boot up vs when it's working. Chances are the disk access from booting the OS is fairly solid activity, whereas when the OS is running, unless it's a very heavy database server (I'm guessing not), the disks will most likely stay fairly idle. If there's any time it's going to fail, chances are it will be on boot up.
Turning your server on and off is a stupid idea. Not only to mention most servers can take upwards of 2-5 minutes to just get past the BIOS checks, it's a huge amount of wasted time too.
2018 Update: Given that most computers are now essentailly entirely solid-state, this answer may no longer be as accurate as it once was. The taxi analogy doesn't really suit todays modern servers. That said, typically you still generall don't turn servers off.
Solution 2:
Turning the server off and on everyday would likely cause it to fail faster than leaving it on.
Solution 3:
The only thing I can see that's even close to right about what you've been told is that drives can fail within 2 years. They can in fact fail at any time. I'm sure most of us have received at least one brand new drive that was DOA. On average server drives will last anything from about 3 years upwards, with 10 or 20 years not being too uncommon. That doesn't mean any individual drive won't fail a whole lot sooner.
Servers (meaning a machine with proper server grade components) are design to run continuously. There is no reason to shut it down at night but some very good reasons to leave it running. Nighttime, or whatever other time is "quiet" for a given system is the time to run all the maintenance and automation.
e.g. Backups are best taken when there is no or little user activity. This helps to ensures backups are consistent. Sure there are ways around this but why not give your backups every chance of success when there is nothing to lose by doing so?
Someone running a "server" with a single disk and no backup is a fool, not an admin. The only reason he got away with it is sheer dumb luck. It had absolutely nothing to do with shutting the machine down at night.
Solution 4:
Servers are meant to operate 24x7. Shutting servers down overnight is extremely non-typical. Server hard drives are designed to be more reliable than desktop drives and now that you have backups and RAID 1, you will not suffer data loss if one of your two drives fails.
What i would worry about now for this 16 years old server is a motherboard or non-redundant power supply failure.
Solution 5:
I've never turned a server off at night before.
Hard drives will fail when they are going to fail. Turning the machine on and off isn't going to make the drive fail slower. I've seen hard drives shipped from the vendor that were already bad, and I've seen disks running (and actively being used) for 5+ years without failing.
Your professors are idiots.