Deferred Error vs. Unit Attention

Peter Cech pcech at
Tue Dec 15 04:39:30 PST 1998

* From the T10 Reflector (t10 at, posted by:
* pcech at (Peter Cech)
I am trying to implement error handling for a certain type
of SCSI device and it seems that there may be a couple of ways to handle
deferred errors.
1) The first and most obvious is by setting the Error Code field to
Deferred Error in the Req. Sense data and returning the necessary Sense
data for the error.
2) Or, you could set the Sense Key field to Unit Attention in the
Sense data and return the necessary Sense data.
It seems to me that these two field can be used to accomplish the exact 
same thing.  Can anyone verify this?? 
Looking at the SCSI spec it seems as though Unit Attention is most
commonly used for Resets, BUT if you read it closely there is an escape
clause which could be interpreted to mean ANY condition, for which a device may
not be able to execute a command, could be considered a Unit Attention. 
Does any one have a feel for what the typical way of handling errors is 
and what the typical use for these two methods are??? 

   Pete Cech   
   Office Imaging Division
   Eastman Kodak Company
   901 Elmgrove Road
   M/S 36010 
   Rochester, NY  14653-36051
   (716) 726-0800
   pcech at nasa.Kodak.COM
   FAX: 716-726-7303
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