What is the definition of the disk status FAILING?

What is the definition of the disk status FAILING?

A.
uncorrectable I/O failure(s) on the public region; private region inaccessible

B.
uncorrectable I/O failure(s) on both the public and private regions

C.
uncorrectable I/O failure(s) on the public region; private region accessible

D.
uncorrectable I/O failure(s) on private region; public region accessible