Date: Fri, 20 Apr 2001 13:33:01 -0700 From: Mike Smith <msmith@freebsd.org> To: Chris Dillon <cdillon@wolves.k12.mo.us> Cc: Domas Mituzas <midom@delfi.lt>, scsi@FreeBSD.ORG Subject: Re: mly driver does not work with SCA in up-to-date 4.3 Message-ID: <200104202033.f3KKX1f02169@mass.dis.org> In-Reply-To: Your message of "Fri, 20 Apr 2001 15:07:47 CDT." <Pine.BSF.4.32.0104201443390.86778-100000@mail.wolves.k12.mo.us>
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> > Basically, CAM insists that things behave exactly like SCSI disks,
> > etc. And RAID arrays just don't; the driver has to fake up all
> > sorts of rubbish like whether the array supports disconnect,
> > tagged queueing, its transfer rate, etc.
>
> I gather this would also cause problems for putting the ATA stuff
> under the CAM umbrella? I thought the idea behind CAM was to be
> somewhat generic in nature, not SCSI-specific.
It may well have been, and in some ways at least the transport layer
probably is fairly protocol-agnostic. However, the current
implementation is hopelessly SCSI-specific, and the peripheral drivers
are not good at dealing with odd situations.
> > I thought initially that because the array uses a subset of
> > SCSI-like commands, it'd make sense. Unfortunately, it doesn't
> > support enough of them to be useful. A wiser compromise would be
> > to have an optional CAM interface that can talk to non-disk
> > devices on the SCSI bus and just interface the disks directly to
> > the bio layer, as I used to do with other drivers.
>
> Would this help out the aforementioned ATA-under-CAM problems?
I used to think that shimming ATA under CAM would make sense; I don't
anymore. Even shimming ATAPI devices under CAM would be a bad idea.
Whilst meaning no offense to Justin and the other CAM folks, I consider
CAM to basically be baggage best avoided unless one has to deal with real
SCSI peripherals.
--
... every activity meets with opposition, everyone who acts has his
rivals and unfortunately opponents also. But not because people want
to be opponents, rather because the tasks and relationships force
people to take different points of view. [Dr. Fritz Todt]
V I C T O R Y N O T V E N G E A N C E
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