Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!cs.utexas.edu!evax!utacfd!merch!cpe!adaptex!adaptx1!neese
From: neese@adaptx1.UUCP
Newsgroups: comp.periphs.scsi
Subject: Re: Command Queueing in SCSI-2
Message-ID: <283400010@adaptx1>
Date: 3 Nov 90 08:25:49 GMT
References: <4297@alliant.Alliant.COM>
Lines: 25
Nf-ID: #R:alliant.Alliant.COM:4297:adaptx1:283400010:000:1243
Nf-From: adaptx1.UUCP!neese    Nov  2 10:02:00 1990


>/* ---------- "Command Queueing in SCSI-2" ---------- */
>Does anyone know if it is possible to start multiple CDBs between one
>initiator and one target in SCSI-2 (so that, for instance, a drive may
>do seek ordering?)  I imagine this would require the ability to
>specify a transaction tag during the disconnect/reconnect messages.
>It does not seem possible in SCSI-1.  Is it possible in SCSI-2?

In the SCSI-1 specification this was not allowed.  It did make provisions
for a target to accept commands from more than one initiator, but no
ordering was spec'd.
In the SCSI-2 spec, a new *optional* feature called tagged queueing is
implemented that allows a target to receive more than one command from
an initiator.  It also makes provisions for sorting and proioritizing
commands in the queue.
It does take both initiator and target to implement this.  But remember,
it is an option in the SCSI-2 spec, so you need to look for it specifically
in the product literature for a device.  FYI:  Our 1740 EISA does implement
the tag queue message when in native (1740) mode.

			Roy Neese
			Adaptec Senior SCSI Applications Engineer
			UUCP @  uunet!utacfd!cs.utexas.edu!
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