In terms of preventing "oops" moments, I'm mainly relying on software (restic) for that, where I trust that (A) backups always append data rather than replacing and (B) it's logic works for marking which data to purge based on rules is accurate. [0]
[0] https://restic.readthedocs.io/en/stable/060_forget.html#remo...
While the local backup service uses an API-key with limited privileges, I need to go back to the bucket/storage-zone settings and see what I can enable, how it would affect total storage, and whether I (with additional privileges) can reliably grab the correct mix of old-blobs to do a restore.
On the other hand, LTO-5 drives are now pretty affordable. And each tape cartridge holds around 2Tb of data for about $20.
I had a smaller setup before, with a simple external LTO-5 drive. Used drives are now are about $300, and you can probably find them cheaper. And LTO-5 is the minimum realistic version, it's the first one that supports LTFS and it has reasonable tape capacity.
Lol, no. "As of today we are closed. Goodbye."
Especially considering what giving even a two weeks now considered "generous".
The probability that the object store goes out of business at the exact time your own copy dies is insignificant.
Or even fancier - just changing the price for the egress.
The probability of a hard drive failure or ransomware at the same time as backblaze or aws going out of business is pretty much not worth thinking about.
The probability of an attacker using the api key in your backup script to destroy the backups is far more possible.
I briefly considered using bluray disks as a backup for my photos and other critical docs. But getting a decent bluray burner seems not so easy these days with most production winding down. Next best thing looks like the "object lock" feature on object store services that prevents deleting objects for a certain time.