Wouldn't this always depend on the length of the queue to access the robotic tape library? Once your tape is loaded it should move really quickly:
https://www.ibm.com/docs/en/ts4500-tape-library?topic=perfor...
Your assumption holds if they still use tape. But this paragraph hints at it not being tape anymore. The eternal battle between tape versus drive backup takes another turn.
For storage especially we now build enough redundancy into systems that we don't have to jump on every fault. That reduces the chance of human error when trying to address it, and pushing the hardware harder during recovery (resilvering, catching up in a distributed concensus system, etc).
When the entire box gets taken out of the rack due to hitting max faults, then you can piece out the machine and recycle parts that are still good.
You could in theory ship them all off to the backend of nowhere, but it seems that Glacier is all the places where AWS data centers are, so it's not that. But Glacier being durable storage, with a low expectation of data out versus data in, they could and probably are cutting the aggregate bandwidth to the bone.
How good do your power backups have to be to power a pure Glacier server room? Can you use much cheaper in-rack switches? Can you use old in-rack switches from the m5i era?
Also most of the use cases they mention involve linear reads, which has its own recipe book for optimization. Including caching just enough of each file on fast media to hide the slow lookup time for the rest of the stream.
Little's Law would absolutely kill you in any other context but we are linear write, orders of magnitude fewer reads here. You have hardware sitting around waiting for a request. "Orders of magnitude" is the space where interesting solutions can live.
[1] https://www.aboutamazon.com/news/aws/aws-data-center-inside
Is tape even cost competitive anymore? The market would be tiny.
The disks for Glacier cost $0 because you already have them.
Last I was aware flash/nvme storage didnt have quite the same problem, due to orers of magnitude improved access times and parallelism. But you can combine the two in a kind of distributed reimplementation of access tiering (behind a single consistent API or block interface).
But then what do you do with the other half of the disk? If you access it when the machine isn’t dormant you lose most of these benefits.
For deep storage you have two problems. Time to access the files, and resources to locate the files. In a distributed file store there’s the potential for chatty access or large memory footprints for directory structures. You might need an elaborate system to locate file 54325 if you’re doing some consistent hashing thing, but the customer has no clue what 54325 is. They want the birthday party video. So they still need a directory structure even if you can avoid it.