Question: Deferred Sense reporting priority

Joseph C. Nemeth jnemeth at
Tue May 5 14:32:05 PDT 1998

* From the T10 (formerly SCSI) Reflector (t10 at, posted by:
* "Joseph C. Nemeth" <jnemeth at>

-----Original Message-----
From: Rodney Van Meter <Rodney.Vanmeter at>
To: 'Jeff Stai' <stai at Brocade.COM>; 'Joseph C. Nemeth'
<jnemeth at>; t10 at Symbios.COM <t10 at Symbios.COM>
Date: Monday, May 04, 1998 4:22 PM
Subject: RE: Question: Deferred Sense reporting priority

> Okay, I'll follow up with a related question.  Forgive me, too,
>if I'm rusty on target implementations, it's been several years since I
>did one.
> How many Unit Attention conditions should the target keep?

Rodney, this whole issue of trying to prioritize and age these errors
through a single sense data block for the LUN has always made my head hurt
so much that I've thrown it out. I keep ALL the UA conditions for ALL the
initiators, for as long as it takes them to show up and claim the UA

This isn't as expensive as it sounds: I need one bit for each UA condition
on each initiator. For a private loop, that's 126 bits, times the number of
UA conditions I want to keep: PON, media removed, mode page changed, etc.

Part of my command pre-check simply tests the bit for each UA condition (in
some order) for that initiator. If the bit is set, I *generate* the UA
condition in the sense data right on the spot, then clear the bit (UA
condition cleared). The bit-mask sits around forever, so any new initiator
will see every UA condition that has ever accumulated for the device.

This obviously doesn't scale well for fabrics, with 2^24 (give or take)
potential initiators, which is why I will eventually need to enumerate the
*actual* initiators that log in, and build my bit mask from there.

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