io_ioctl: ioctl (MTWEOF) failed on media id DT00xx, drive index 0, I/O error (bptm.c.9796)

Some tape libraries can require an annual service, and the term for this is PM, or 'Preventative Maintenance' - whereby the mechanical gearing of a library robot arm is cleaned and re-greased, and then re-aligned.  An engineer performing PM shoudl also inspect for worn gears, worn motors, loose drive belts, replace air-filters, and clean any light residual traces of grease, grime and dust from within the inside of the tape library, and clean the bar-code laser and 'eye/lens'.

Some libraries can be rebooted so that, as part of their reboot process, they use special (hidden from NetBackup) bar-coded points within the library chassis to re-align themselves internally, so that the robot arm lines up correctly with the fromt of teh tape drives - this process is sometimes referred to as 'Library learn' sequence.

So more modern libraries are more advanced and no longer require any annual PM, as they are self lubricating, and self adjusting.

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Maybe it's been a while since your library was serviced, or had PM.