Wrong. Movies and music are generally already compressed and 7zip or other similar file compression tools won't do much besides waste your time. That's why you should generally turn off backup compression on video and music backups.

There's no reason to be backing up 20TB of data if you're not Amazon or Google. Separate out the essential data that you can't live without. Your music collection, your work files and your photos. The rest is disposable. Then go get yourself 2 nice identical hardware RAID cards, set up a 4+ drive RAID5 fileserver using 1.5 or 2TB drives, with 3 active drives and one drive as a hot spare. Buy at least one extra drive for when you need to put your hot spare into action and replace a dead drive. Put all your important data on that raid, put it in a closet somewhere, put in a ventilation fan of some sort, set up email alerts to tell you when there's SMART errors or the raid is degraded, then check your raid status software once a month just to be sure it's all good. Then get another cheap external RAID enclosure with built-in raid5, (something like a StarTech SAT3540U3ER - which is iffy, but works for me) and fill it with 3TB or 4TB drives (plus another spare for when THAT raid fails) and use that to back up your first raid. The backup raid should be large enough to hold at least 2 full backups of the first raid -- choose your drive sizes accordingly. Then back up your first raid onto the 2nd and smile because you've finally achieved relative safety for your important data. Then take a deep breath and say to yourself "I can live without all those videos if something goes wrong. It will suck, but it won't be life-ending, after all that's what bittorrent is for". If you know where to go, you can find almost any movie or tv show and download it in under an hour via bittorrent. Hell, you can download 15 seasons of South Park in h264 format in under an hour. Most HD movies in 1080p format take 30 minutes or less over a decent connection. And if you really care about saving your videos, make an offline library and burn them to DVDs. Not really feasible if you've waited until you filled 20TB of drive space with movies and tv shows, but I have a series of 4 filing cabinets with DVD-sized drawers full of around 2000 CD-Rs and DVD+Rs (and a few BD+Rs for my 170GB collection of BBC Horizon documentaries) I've burned since about the year 2000 when DIVX and XVID format movies started to appear en masse. Every few months I'd spend an evening or two burning my latest batch of movies to DVD and then removing them from my hard drives. But I've found that most of the time these days I don't even touch my archives when I want to watch one of my movies because it's easier just to download a fresh copy in 1080p which is generally better than the archived version I downloaded years earlier. I expect that trend will continue, which is why I've recently stopped burning my movies altogether and now I just add hard another shared hard drive to one of my HTPCs as they fill up, or delete stuff I know I'll never watch again. And last, but not least, I'd be remiss if I didn't mention unRAID. Though I don't use it myself because I've long-since gone down the path of the aforementioned RAID5 setup, unRAID could be the best option if you're starting from scratch. unRAID gives you RAID5-like redundancy, but with arbitrary disks, and with the benefit of only losing the data from specific failed drives in the rare event that it can't be rebuilt from parity data. If you want to know more about unRAID, google it. And forget about backing up 20TB of data for at least another 5 years. No one has that kind of time.

The page you linked to contains the Trojan:JS/Gamburl.E. MSFT Security Essentials just flagged it and removed it from my browser cache.

I always run 3 antivirus progs on my PC and have found the following setup to work fine with minimal impact on system performance:

1. ClamwinAV - The gold standard for linux server admins, ported to Windows - the smallest memory footprint of any of them and doesn't interfere with other antivirus progs.
2. Avast - You're crazy if you think it's any harder to get their free version than it ever was. You've always had to re-register for a new key every year. Been using it for over 5 years. Other posters are correct, the voice that alerts you to your daily updates really kills the mood when you're trying to get jiggy with your lady friends. I always turn off that voice first thing.
3. Microsoft Security Essentials - This also runs fine with the other antivirus progs.

The only caveat I've found running these 3 progs together is that sometimes one virus prog will flag the automatic virus updates of another prog and try to quarantine them, but all you have to do is add the relevant folder to the list of excluded dirs in whichever program flags the updates. About once a year (or whenever I disregard my own security knowledge and download some infected software), I run several anti-malware progs (spybot,adaware,etc.) and also run a trial of whatever seems like the highest rated commercial antivirus product at the time. This year it was Avira, which I'm still running, but getting sick of the daily pop-up ads. Avira recently did a great job of removing a pesky trojan that other progs had trouble with after I installed an infected bittorrent download. So right now I'm actually running Clamwin, Avira and MSFT Security Essentials. The only time it bogs down my system is when doing a full scan, but that's to be expected.