[9366] in linux-scsi channel archive
Re: shared SCSI buses
daemon@ATHENA.MIT.EDU (David Teigland)
Fri Aug 11 12:22:46 2000
Date: Fri, 11 Aug 2000 11:16:04 -0500
From: David Teigland <teigland@sistina.com>
To: Mark Veteikis <mark@iphase.com>, Kurt Garloff <garloff@suse.de>,
Chris Meadors <clubneon@hereintown.net>,
Martin Peschke <peschke@fh-brandenburg.de>
Cc: linux-scsi@vger.rutgers.edu, gfs-devel@sistina.com
Message-ID: <20000811111604.A15939@sistina.com>
Mime-Version: 1.0
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In-Reply-To: <200008111435.JAA22792@sw10.Iphase.COM>; from mark@iphase.com on Fri, Aug 11, 2000 at 09:35:19AM -0500
On Fri, Aug 11, 2000 at 09:35:19AM -0500, Mark Veteikis wrote:
> >
> >
> > I'm interested in combining two or more active hosts with multiple devices
> > on a single parallel SCSI bus. I've successfully done this, but don't know
> > the extent of problems which could arise when hosts or disks are added or
> > removed (crashed) on the in-use bus.
> >
> > A) How likely is it that the scsi driver(s) will see errors when nodes and
> > drives come and go and are there specific cases which are bad?
> >
> > B) What are the possibilities of a node surviving if it sees scsi errors?
> >
> > C) How much work would it take to make all these odd cases reliable?
> >
> > I'm interested in the status on both 2.2 and 2.4. Thanks.
>
> Have you looked at Fibre Channel? Linux has support. Or are your target
> devices/HBAs locked into SCSI?
Thanks to all for the input. I should have provided some more background
information. I work on the GFS project and we primarily use Fibre Channel. I
know SCA parallel SCSI drives are the way to go, but it still sounds like a
touchy issue. I've seen my share of scsi mid-layer errors which lock up
the machine, so I wanted to try and get a clearer picture of things.
- Hot-swapping SCA disks on the bus should be relatively reliable if it's done
with care. It sounds like if any transfer is happening during a swap you're
in serious danger of crashing everthing. The scsi drivers can be prompted to
add or remove devices. I wonder if multiple hosts put a wrench in things
here.
- The other important issue is hosts which crash at any time, including during
a transfer. It sounds like the drivers on other machines will currently
start a reset-war, but the drivers could be improved to avoid this and
hopefully keep using the devices as they were.
- A similar problem for devices which crash abruptly.
- How about adding machines to the bus and then booting them up?
By the look of things here, it is not reasonable to use GFS with multiple hosts
on a shared SCSI bus if you're interested in HA. If any machine or disk
crashes, all your devices are probably in trouble. Stopping all machines' I/O
(and maybe unmounting everyone) to add or remove storage would also be
prohibitive.
Thanks.
--
Dave Teigland <teigland@sistina.com>
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