You’ve linked into it, but I was just going to point at the Git book: https://git-scm.com/book/en/v2
It’s an afternoon’s reading; it does an excellent job of giving you the right mental model - and a crib aheet of commands to navigate it.
Figure eight on a bight.
The other thing to watch out for is if you’re splitting state between volumes, but i think you’ve already ruled that out.
I’d be cautious about the “kill -9” reasoning. It isn’t necessarily equivalent to yanking power.
Contents of application memory lost, yes. Contents of unflushed OS buffers, no. Your db will be fsyncing (or moral equivalent thereof) if it’s worth the name.
This is an aside; backing up from a volume snapshot is half a reasonable idea. (The other half is ensuring that you can restore from the backup, regularly, automatically, and the third half is ensuring that your automated validation can be relied on.)
Ed Balls