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Date:      Mon, 7 Feb 2000 14:48:04 -0700
From:      "Kenneth D. Merry" <ken@kdm.org>
To:        Gerard Roudier <groudier@club-internet.fr>
Cc:        Wilko Bulte <wilko@yedi.iaf.nl>, George Morgan <gemorga2@vt.edu>, freebsd-scsi@FreeBSD.ORG
Subject:   Re: Rescan for Devices...
Message-ID:  <20000207144804.A24368@panzer.kdm.org>
In-Reply-To: <20000207143833.A24212@panzer.kdm.org>; from ken@kdm.org on Mon, Feb 07, 2000 at 02:38:33PM -0700
References:  <20000207191037.A386@yedi.iaf.nl> <Pine.LNX.3.95.1000207221417.341A-100000@localhost> <20000207143833.A24212@panzer.kdm.org>

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On Mon, Feb 07, 2000 at 14:38:33 -0700, Kenneth D. Merry wrote:
> On Mon, Feb 07, 2000 at 22:55:33 +0100, Gerard Roudier wrote:
> > I guess the reasons given that xpt_scan_bus() is scanning targets
> > (excepted the initiator obviously) in parallel. I would think that such a
> > concurrent target scanning can be faster than a sequential scanning, only
> > if some devices, that are too long for responding to SCSI commands used
> > for the probe, (probably INQUIRY) disconnect the BUS during the scan. But
> > if this happens, or if some devices are reporting transient problems, then
> > order of devices cannot be guaranteed on successive (reboots) + (re)scan
> > of BUS.
> > 
> > In my opinion, an option that will allow to request a sequential BUS
> > (re)scan would be useful, not only for me. 
> 
> Devices are attached sequentially, unless you hard-wire them.  If you
> rescan the bus, though, the disks are given the first available device
> number.
> 
> If you want things to turn up in the same place every time, I would suggest
> hardwiring your disk device numbers to a specific bus/target/lun.

BTW, devices not probing in sequential order during a rescan is a known
bug.

You might want to file a PR, and then assign it to Justin.  (He said it's
on his list of things to fix.)

Hardwiring should work around the problem, however.  Hardwiring might be
broken in -current, though, some people on the current list are complaining
about it.

Ken
-- 
Kenneth Merry
ken@kdm.org


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