Write incompatibility

Hallam, Ken MV KHallam at po2.mv.unisys.com
Wed Sep 25 11:06:00 PDT 1996

* From the SCSI Reflector (scsi at symbios.com), posted by:
* "Hallam, Ken                 MV" <KHallam at po2.mv.unisys.com>

SCSI Mavens,

There is a situation operating tape drives, (or any removable media device) 
wherein a new device will read, but not write older generation media. Only 
newer media can be both written and read on this device. The question for 
our mavens is thus: Given a new device that has older media mounted, what is 
proper SCSI etiquette to use as a response when the host sends down a WRITE 
command to media than cannot be written?

Possible Responses:
A. Check Condition 02, Sense Key 5h, (Illegal Request)) ASC/ASCQ 30h/05H 
(cannot write medium, incompatible format)
B. Check Condition 02, Sense Key 3h, (Medium Error), ASC/ASCQ 30h/05h

The Sense Key is the area of contention. A Key of 5 says illegal request, 
but the SPC definition indicates that this code is related to errors in 
"bits in the CDB" and since there were no invalid bits in the CDB, this code 
seems less than perfect.

A Key of 3 is defined as a Medium Error, but this is normally taken as 
pointing a specific defect on the recording media itself, which is not the 
case here thus, Sense Key 3 does not seem to fit either.

We have vendors who argue for either Sense Key value. Is there anything 
approaching a consensus out there?


Ken Hallam
ken.hallam at mv.unisys.com
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