This thread just reminded me that it's been a bit over a month since I did the manual drive updates, and since it's the beginning of a new year, I decided to do both a manual full HD backup plus the backup of all photos last night, so all shots through 12/31/17 are now updated and saved on the externals.
I've always kept a fire safe around for the passports and special docs, and it fits the small portable drives just fine. I used to use tapes as well at work, but as you say, too small. The portables at 2TB are super cheap, and the 4TBs are around $100ish - so prices aren't bad at all. I use a 2TB for just the photos, and the 4TB for the full drive. May need to upgrade the 4TB full drive though, as I'm running around 3.6TB used now.
I also have a firm 'cleanup' process where I go back through older photo folders and clean out shots I never processed or used...after a few years, I like to run through those older folders and find originals that I never processed, and make a decision if it's worth keeping or not - by cleaning out older photos that I'll never use, I can reduce by about 150-200GB each year (in Dec 2017, I cleaned up 2015 folders...next year, I'll clean up 2016). Since I have photo folders going back to 1997, it's helped to keep those cleaned up before I do the year-end backups!