> Blu-ray, or any non-rewritable optical media, guarantees that it hasn't been tampered with.

In terms of external tampering, I think that need is better-served by encrypting everything, which you probably want to do anyway. Or at least using some sort of checksum signed by a key.

However if the focus is "what if the backup process is compromised", then yes, having some date which is beyond its writing-reach may be useful. Another aspect of this might be a remote-backup system where one set of credential is enough for daily backups and restore, while another is needed in order to access a set of older duplicates that are remotely maintained as ransomware-protection.

That depends on your threat model. If the attacker can swap the Blu-ray disc to a similar looking one, but with content they control, that absolute guarantee becomes moot.

Used Tape drives often had the write heads service hours go well past its recommended limits. Mission critical IT systems don't get "upgraded" off schedule very often. ymmv

Anecdotally, I have seen Tape sets fail in production settings, as a remote office location admin was doing incremental backups... and the sick tape drive kept silently damaging each daily roll-back attempt. They may fail ungracefully in an archival context.

I do not deny a janky BD-R drive option is situation specific, but for small projects I am fine with a 25GB disc $25.80/TiB solution with the occasional big file $62.42/TiB hit for 100G/128G EOL discs.

HDD are less hassle, still hit below $34.63/TiB, and last a few years. Not a bad fall back option if you still have old inventory. =3

It isn't too expensive for my use case – per month, I retrieve about 500GB a month from Glacier Instant Retrieval to verify, which costs ~$15. Combined with other costs, my monthly bill is ~$50.

I used to use Backblaze B2, which had cheaper egress at the cost of slightly more expensive storage (I think ~$5/TB/mo, with free egress up to 3x all current storage?) So I paid $20. But at some point AWS opened a datacenter near me, and I couldn't ignore how much faster data transfers got.

Depending on the amount of data you have, might it not be less expensive than build the tape drive?

An LTO drive is easily $10.000. You can restore a lot of S3 data for that amount of money. Sadly getting cheaper tape options is not really possible anymore.

use cloudflare's r2, no egress fees