The default tier of AWS glacier uses tape, which is why data retrieval takes a few hours from when you submit the request to when you can actually download the data, and costs a lot.
AFAIK Glacier is unlikely to be tape based. A bunch of offline drives is more realistic scenario. But generally it’s not public knowledge unless you found some trustworthy source for the tape theory?
Perhaps I’m misremembering things, but I’m pretty sure the SysVinit didn’t run any “more restricted processes”. It ran a bunch of bash scripts as root. Said bash scripts were often absolutely terrible.