Date: Fri, 20 Apr 2001 12:38:37 -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: <200104201938.f3KJcbf01621@mass.dis.org> In-Reply-To: Your message of "Fri, 20 Apr 2001 11:25:13 CDT." <Pine.BSF.4.32.0104201118540.80885-100000@mail.wolves.k12.mo.us>
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> On Thu, 19 Apr 2001, Mike Smith wrote:
>
> > I *knew* that interfacing this driver to CAM was a bad idea, and I
> > was right. 8(
>
> I'm kinda glad you did, since when I had to pull the Mylex controller
> when I could no longer get the system to boot, I just hooked one of
> the disks from the RAID1 array onto a regular SCSI controller and
> never had to edit fstab since the device name never changed. Its only
> a minor advantage, I know. What is it about CAM that doesn't fit well
> with what you're doing?
This, just for starters. 8)
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 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.
--
... 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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