One of my NetBSD machines has chosen to utter this:

sd0(ahc1:0:0):  Check condition on CDB: 0x28 00 00 44 e8 32 00 00 10 00
    SENSE KEY:  Hardware Error
     ASC/ASCQ:  Diagnostic Failure on Component 0x01
     FRU CODE:  0x3

I assume that "FRU CODE" tells me what field-replaceable unit is bad.  
But I don't know what '0x3' refers to.  My guess is that it's the 
controller, since the disk is both new and was installed in response to 
previous indications of hardware failure.  (The drive is a Seagate 18G 
ST318461W; the controller is an Adaptec AIC-7890 on the motherboard.
The machine is running NetBSD 1.5.2.)

		--Steve Bellovin, http://www.research.att.com/~smb
		Full text of "Firewalls" book now at http://www.wilyhacker.com