That's just showing that there isn't a RAID array defined for the compact flash. I see the same thing on a working 8900:
Sys::Raid::Disk
Name Serial Number Array Member Array Status
------------------------------------------------------
CF1 B85131BGBCR209131600 no undefined
HD1 WD-WCAT18687337 yes ok
HD2 WD-WCAT18687750 yes ok
Which platform is this? Have you seen SOL12170:
sol12170: The BIG-IP system may use the CompactFlash card for the swap partition on some platforms
http://support.f5.com/kb/en-us/solutions/public/12000/100/sol12170.html
You could force an disk check following SOL10328. You might also try running qkview and uploading the tech.out to
http://ihealth.f5.com to review the suggestions there. If you don't get anything useful there, you could open a case with F5 Support.
Aaron