Compex Systems Advanced SerialRAID Adapters SA33-3285-02 - Manual (Page 127)

exposed
One member disk drive of a mirrored pair is missing or has failed, but no
write operation has been issued to the pair.
degraded
One member disk drive of a mirrored pair is missing or has failed, and a
write operation has been issued to the working member disk drive.
rebuilding
A failed member disk drive in a mirrored pair has been exchanged and
data is rebuilding.
offline Both member disk drives of a mirrored pair are missing or have failed.
Chapter 6. Using the RAID Array Configurator 107