parity checking option jumper

Gerry Houlder Gerry_Houlder at
Thu Apr 24 15:23:41 PDT 1997

* From the SCSI Reflector (scsi at, posted by:
* Gerry Houlder <Gerry_Houlder at>
Francesco Ceci <f.ceci at> asked:
>I'd like to know what the Scsi specifications recommend about the parity 
generation and checking.
>By experience, I know that all Scsi devices generate the parity, while the 
parity checking is normally >controlled by a jumper that allow to 
enable-disable it.

My reply:

The SCSI standard is silent about the operation of the parity checking jumper. 
It only says that the checking of parity and generation of parity was optional 
in SCSI-1, mandatory in SCSI-3, and probably optional in SCSI-2. SCSI-1 also 
suggested that all devices must to it the same (if one device is not checking 
parity, the rest shouldn't either). If you follow this guideline, the jumper 
can disable generation of parity as well as checking of parity.

My advice is to always use it with parity enabled - this behavior is clearly 
defined in the standards and is the "mainstream" behavior.
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