As a follow on question, was it common for more important people, such as noblemen or knights to have servants or attendants clean their mail and/or other gear for them, or was there a culture that expected soldiers to care for their own equipment as there is in the modern military?

I'll narrow my time and place to Saxon england of the 10th century, but I'm interested in all answers of times and places were chainmail was still worn.

I hope someone has information on cleaning and maintenance of this type of gear! I know the boring and uninteresting portion of warfare often gets overlooked in pop media, but as a former soldier I know that (to exaggerate) cleaning your crap is basically a way of life, and as an afterthought sometimes you fight!

Was the process of rolling the armour in a barrel full of sand really used?

Yes, that tactic really was used. If there no barrel and sand happened to be handy at the moment, another common method was some sort of sack with sand/vinegar (and I've heard SCA guys say urine, too. ick), and it'd be vigorously shaken and moved around, and then oil re-applied.

Really though, the key to keeping armor free (well, mostly free) of rust was preventative maintenance. Keeping maille oiled made it a fairly messy affair, but a hauberk or byrnie that was oiled and then worn against a gambeson (thick, padded jacket) would cause it to rub around on itself, which is a sort of continual light-duty scrubbing.

A lot of metal armor would also be blued, via either the hot or cold method. "Hot" bluing involves quenching heated metal in oil, which sort of suspends a protective coating on the outer surface of the metal, so nothing underneath it can rust. Of course, the method isn't totally 100% rust-proof, it only slows rusting down. Periodic cleaning and re-oiling would be necessary. Medieval armor was made from high-carbon steel, so frequent care and cleaning were pretty important.

"Cold" bluing involves flash-rusting the metal with something like urine, making sure there's a nice, even coverage. Then, everything's coated with oil, which impregnates all of the little surface imperfections. Then they'd let it sit for a while, lather, rinse, repeat. The finish from cold-bluing isn't blue. Dark, black/brownish hues are more common.