Why can't we read customer data when the heads are unable to write?

[osity]

We often encounter heads that are able to read the SA without any problems. When we test the heads by trying to write to a log file, they are unable to write.
Why does this writing limitation affect our ability to read the data?

[Takanashi_Hina]

Maybe because there are instructions to test the heads on the ROM code and if the heads don't pass the internal test the drive doesn't even load the translator ?

[DataMedics]

Yes, and I suspect it varies between specific models why it won't work. The drive likely may be trying to perform background processes such as S.M.A.R.T. logging to update power on cycles, run hours, etc. and when it fails to write the updates to the logs goes into an error state. Unfortunately, HDD manufacturers don't give a hoot about the data recovery side of things.

I've got an 8Tb Seagate here now that I can't seem to get anywhere with because it won't write even with perfectly matched donor heads from a drive the customer bought the same day. It's very annoying knowing that the heads are reading fine, but you can't access the data because the firmware just won't let you.

[osity]

When I do the head test from the service area menu, the head that can't write has no problem passing the test. It's frustrating.
Datamedics, What are you going to try on that 8TB, since it can't write? Your case does not seem like a head issue.