If you use F1 (Help) on the display you will see in the help text:
Indicates that a decrease in performance has occurred because a
component that is not critical has failed. No data is lost due
to this failure, but the damaged unit needs to be repaired or
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It could be your cache battery needs replacing.
Disk degraded might be caused by some hardware errors or incompatibility issues. You to carefully make sure that the disk is compatible with other hardware parts of the computer system.