A super-bad idea because drives made on the same week in the same facility will all fail at the same moment.

With respect, I just went through a "code red" at a large, well-known cloud storage company caused by synchronized late-life death of hard disks all manufactured in the same batch. That's the second time in my career that I've been through the same phenomenon. Hard disks that are made together wear out together.

I can confirm this. I learned the hard way to buy hard disk drives of the same model but from different batches.

I'm curious how wide the failure window was (timespan, ramp-up/down, etc), relative to how many devices were involved.

And I wonder how well the signal in that ratio might scale down to hundreds or tens of disks.

Shockingly bad production engineering then.

Not once, but twice:

https://www.techradar.com/news/new-bug-destroys-hpe-ssds-aft...

"Hewlett Packard Enterprise (HPE) has once again issued a warning to its customers that some of its Serial-Attached SCSI solid-state drives will fail after 40,000 hours of operation unless a critical patch is applied.

Back in November of last year, the company sent out a similar message to its customers after a firmware defect in its SSDs caused them to fail after running for 32,768 hours."

Can you imagine provisioning and deploying a rack or 3 full of shiny new identical drives, all in RAID6 or RAID10, so you couldn't possibly lose any data without multiple drives all failing at once...

(Evidence that the universe can and does invent better idiots...)

Your default assumption only works if every disk has an independent probability of failing from each other. Which is definitely not true if you buy all the disks from the same batch.

Others have mentioned the problems with this strategy, but getting drives with the same firmware is done routinely to avoid having slightly different behavior in the RAID set.