[4931] in linux-scsi channel archive
Re: dual-attached disk
daemon@ATHENA.MIT.EDU (Leonard N. Zubkoff)
Sat Oct 17 09:24:20 1998
Date: Fri, 16 Oct 1998 14:39:21 -0700
From: "Leonard N. Zubkoff" <lnz@dandelion.com>
To: sct@redhat.com
CC: thoth@purplefrog.com, linux-scsi@vger.rutgers.edu
In-reply-to: <199810161112.MAA02484@dax.dcs.ed.ac.uk> (sct@redhat.com)
Date: Fri, 16 Oct 1998 12:12:36 +0100
From: "Stephen C. Tweedie" <sct@redhat.com>
On Tue, 13 Oct 1998 09:55:26 -0400, thoth@purplefrog.com said:
> Does Linux support dual-attached SCSI drives? We have an
> application where we'd like to take some disk and use it from one
> machine, and if that machine fails, mount the disks on the other,
> and resume serving data. In the Sun world, you just run a SCSI
> chain out of one machine and into another. Can Linux do this?
It's more of a driver issue. I have heard of people doing exactly
this on Linux with certain SCSI drivers, and other people getting
nowhere with a different driver. Common problems are things like bus
resets: if a driver doesn't like an unexpected bus reset and responds
by resetting the bus itself, you get an endless ping-pong of bus
resets between the two controllers which kills the bus dead.
Ability to share a SCSI bus is primarily a matter between the driver and host
adapters. Some host adapters cannot handle being selected by another
initiator, which makes operating in a multi-initiator environment impossible.
Drivers must avoid reset wars when detecting an external bus reset caused by
the other host adapter as you noted.
The BusLogic driver should support a multi-initiator environment and I even
tested mounting a read only file system on two machines at the same time. To
make this work, you need to use the BT-948, BT-958 or BT-958D (not the
FlashPoints) and:
(1) Set one of the two host adapters to a SCSI ID other than the default of 7.
Typically 6 is a good choice.
(2) Disable the BIOS scan on both host adapters.
The upshot of (2) is this should not be the boot controller.
Leonard
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