RE>Re- SCSI-3 Reseved Field

jmcgrath at jmcgrath at
Thu May 5 10:22:47 PDT 1994

        Reply to:   RE>Re: SCSI-3 Reseved Fields a

I agree with your thoughts, but one of the reasons the customer would cite not 
checking reserved bits as a problem is the SCSI standard, that implies you MUST 
do reserved bit checking.


Date: 5/4/94 5:26 PM
To: Jim McGrath
From: roys at

While I agree that the checking of reserved fields is a cumbersome task, and it 
be nice not to have to do so, based on experience, there are some practical 
that should be taken into consideration.

Consider the senario where drive company A (who chose not to do reserved field 
is competing against drive company B (who implements this checking and reports 
CONDITION if a reserved bit is not set to zero), for a large volume contract at 
company C.

Company C will run both competing drives through an array of tests, including 
specific drive
testing, and system testing.  At some point in these tests the fact that drive A 
does not 
(and that drive B does) report CHECK CONDITION when a reserved bit is non zero 
will be
noticed and reported.  Guess which drive company's management gets told there is 
a problem,
and which drive company's engineers will be working weekends until drive A 
operates just likedrive B?

Now maybe drive company A could argue that it's drive's performance will be 
better than
drive B due to not having to check reserved bits, but maybe some of C's 
customers also do
qualification testing that would notice this difference, so that this argument 
will not
satisfy C.

In summary, it seems to me that making the setting of reserved bits equal to 
zero mandatory, but the checking of the same reserved bits optional could lead 
to some potential problems.


Roy Shenfield
Senior Staff Engineer
email roys at

These opinions are mine only and do not reflect any company position. 

More information about the T10 mailing list