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Date: Wed, 17 Oct 2001 10:55:35 -0700
From: "Jeff V. Merkey" <jmerkey@vger.timpanogas.org>
To: Kai Makisara <Kai.Makisara@kolumbus.fi>
Cc: linux-kernel@vger.kernel.org, jmerkey@timpanogas.org
Subject: Re: SCSI tape load problem with Exabyte Drive
Message-ID: <20011017105535.C24698@vger.timpanogas.org>
In-Reply-To: <20011016153623.A21324@vger.timpanogas.org> <Pine.LNX.4.33.0110170935300.2271-100000@kai.makisara.local>
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In-Reply-To: <Pine.LNX.4.33.0110170935300.2271-100000@kai.makisara.local>; from Kai.Makisara@kolumbus.fi on Wed, Oct 17, 2001 at 09:43:42AM +0300
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On Wed, Oct 17, 2001 at 09:43:42AM +0300, Kai Makisara wrote:
> On Tue, 16 Oct 2001, Jeff V. Merkey wrote:
> 
> >
> >
> > On 2.4.6 with st and AICXXXX driver, issuance of an MTLOAD command
> > via st ioctl() calls results in a unit attention and failure of
> > the drive while loading a tape from an EXB-480 robotics tape
> > library.
> >
> > Code which generates this error is attached.  The error will not
> > clear unless the code first closes the open handle to the device,
> > then reopens the handle and retries the load command.  The failure
> > scenario is always the same.  The first MTLOAD command triggers
> > the tape drive to load the tape, then all subsequent commands
> > fail until the handle is closed and the device is reopened and
> > a second MTLOAD command gets issued, then the drive starts
> > working.
> >
> This is a "feature" of the st driver: if you get UNIT ATTENTION anywhere
> else than within open(), it is considered an error. In most cases this is
> true but MTLOAD is an exception. I have not thought about this exception
> and noone before you has reported it ;-)
> 
> As you say, the workaround is to close and reopen the device after MTLOAD.
> You should not need the second MTLOAD.
> 
> I will think about a fix to this problem. The basic reason for not
> allowing UNIT ATTENTION anywhere is that flushing the driver state
> properly in any condition is complicated and there has been no legitimate
> reason to allow this. However, here it should be sufficient to use a no-op
> SCSI command after LOAD to get the UNIT ATTENTION.
> 
> 	Kai
>

Kai,

Thanks for the prompt response.  We will continue using the current
recovery method since this appears to work based upon your 
description of what is happening here.  I will remove the second MTLOAD 
command and test with the robotics library.  Sounds like it should
work OK.  Please let us know what you decide if you feel a workaround
is needed for this problem, and we will be happy to test it for 
you.

Do-na-da Go-hv-e

Wa-do

Thanks

Jeff
 
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