the definition of a drive that has died, is one that will not provide Disk Utility with BOTH
its appropriate make&model AND
a reasonable non-zero size/capacity.
Such a drive can not be Repaired, Erased, or used with its current connection method.
When you run Disk Utility, it checks the Disk Directory, and ONLY the Directory, for integrity and self-consistency. It does not read ANY data blocks, at all.
So to find the complete picture of the health of a modern drive, other methods must be used. These methods depend on a feature of modern SATA and later drives. These features fall into the class of SMART status.
When a block is found to require substantial re-reading and error-correction, or a block can no longer be read in 1,000 re-tries, the drive controller 'takes names'. Those block numbers are put on a drive controller's list of questionable blocks, so that they can be examined in detail later.
So one way to check a drive's health is to read out the full SMART status, and check the parameter (among others) called "Current Pending sectors" which tells us how long is the list of marginal blocks that have yet to be resolved. A popular solution for Macs today is DriveDX by BinaryFruit, a low cost/no cost Utility.
Drives carry spare blocks, that are substituted for blocks found to be bad. Suffice it to say that drives can heal a MODEST number of Bad Blocks, but only when NEW data are written to marginal blocks. when a drive runs out of spare blocks, initialization and disk writes failing you get errors.
The other way is the erase the drive, and re-install something complicated onto it. Say, something with more than 350,000 files in it that takes up more than 20 GB. That would be some version of MacOS . Erasing a modern rotating Magnetic drive only literally erases the section that will soon hold the directory. The rest of the blocks are unchanged. Only be re-writing MANY files can we determine whether the drive is good and seems to be staying good.
If you erase a drive and re-install MacOS and the files don't "stick" and appear and behave properly, the drive is very likely to be bad. At least Bad enough that it can no longer be trusted with your precious data. That is, after all, the real metric of whether a drive is working adequately for your use.
