Enormous course failing automated backups

Hi all.

I am running 2.6.

We are building a Moodle course that contains MP3 audio for an entire library of graded readers (short, easy books for language learning) so that students can listen along as they read.

We're talking about many gigs of MP3s.

For legal reasons, I have to have them inaccessible from the web, so I have been adding them to Moodle so they are locked away in the DB and only our students can get to them.

However, this has resulted in the automated backup of that class being unable to finish. I imagine it's simply timing out, but I think I would have to set my PHP max time to something like 12 hours or something to enable it to actually finish, and I think that would cause more problems that it's really worth.

In the meantime, I suspect that the other classes won't be able to run their backup this evening (backups run in the middle of the night on Saturday/early Sunday), as I have been receiving an email every 2-3 hours from my server telling me, "Some of your courses weren't saved!!"

I've been reading the forums and the wiki on this, but I am not sure how to proceed. Some questions for anyone more knowledgeable:

1. Does anyone have a rule of thumb for how long it takes to back up a certain amount of data? Once we have all this stuff uploaded, this course will never change again, so if I get one backup of it, by letting PHP take the necessary time, then I can probably back my settings back down after.
   
2. Is there a way I can just flag this course not to be backed up? We're still uploading to this, and now that classes have ended, work will slow way down without slave student labor to exploit to get it done. If I could get the automatic backup system to just ignore it for a few weeks, that would help a lot.
3. Any better ideas for hosting this stuff in a way that only our users can get at it? I saw someone else with a big course on these forums talk about using a repository, but budget for this is zero (recurring charges are almost impossible to get covered), and I think it's about 10GB we're talking about here. I thought about just sticking it in a directory on the server, but I'd probably have to have it in the webroot, and then we're back in trouble with copyright...

Hope someone has some good ideas... Especially for clever ways to keep this out of the database entirely, while ensuring that only Moodle can get to it.

ADDENDUM: What about a local webDAV directory? And if I did that, how do I make sure I got all the MP3s out of the database? There are some posts around here complaining that even after killing all references to uploaded files, they still live in the DB, bloating it...