From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Anderson Subject: Re: aic7xxx sets CDR offline, how to reset? Date: Wed, 4 Sep 2002 10:13:22 -0700 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <20020904171322.GA1645@beaverton.ibm.com> References: <10209040040.ZM49716@classic.engr.sgi.com> <200209041624.g84GOJC02683@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <200209041624.g84GOJC02683@localhost.localdomain> List-Id: linux-scsi@vger.kernel.org To: James Bottomley Cc: Jeremy Higdon , Doug Ledford , Alan Cox , "Justin T. Gibbs" , linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org James Bottomley [James.Bottomley@steeleye.com] wrote: > jeremy@classic.engr.sgi.com said: > > For example, in Fibrechannel using class 3 (the usual) > > > send command (command frame corrupted; device does not receive) > > send barrier (completes normally) > > ... (lots of time goes by, many more commands are processed) > > timeout original command whose command frame was corrupted > > This doesn't look right to me from the SCSI angle I don't see how you can get > a successful disconnect on a command the device doesn't receive (I take it > this is some type of Fibre magic?). Of course, if the device (or its proxy) > does receive the command then the ordered queue tag implementation requires > that the corrupted frame command be processed prior to the barrier, this > isn't optional if you obey the spec. Thus, assuming the processor does no > integrity checking of the command until it does processing (this should be a > big if), then we still must get notification of the failed command before the > barrier tag is begun. Obviously, from that notification we do then race to > eliminate the overtaking tags. In FC class 3 if you are logged into a port then notice of this loss doesn't happen until a upper level timeout occurs (ULTP?). The loss can happen prior to the command reaching the device (i.e. the switch can drop the frame). If a corrupted frame makes it to the device it will be discarded as there is not much it can do with a frame containing unreliable data. In FC class 2 frames are ack'd so the recovery can be much more responsive. -Mike -- Michael Anderson andmike@us.ibm.com