Date: Fri, 20 Apr 2001 23:29:57 -0600 From: "Kenneth D. Merry" <ken@kdm.org> To: Chris Dillon <cdillon@wolves.k12.mo.us> Cc: Mike Smith <msmith@FreeBSD.ORG>, 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: <20010420232957.A69868@panzer.kdm.org> In-Reply-To: <Pine.BSF.4.32.0104201443390.86778-100000@mail.wolves.k12.mo.us>; from cdillon@wolves.k12.mo.us on Fri, Apr 20, 2001 at 03:07:47PM -0500 References: <200104201938.f3KJcbf01621@mass.dis.org> <Pine.BSF.4.32.0104201443390.86778-100000@mail.wolves.k12.mo.us>
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On Fri, Apr 20, 2001 at 15:07:47 -0500, Chris Dillon wrote: > On Fri, 20 Apr 2001, Mike Smith wrote: > > > 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 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. Not really. The ATA model is generic enough that we would probably do something like write a specific ad-type peripheral driver to talk to ATAPI disks. ATAPI CDROM drives may be enough like SCSI CDROM drives that they could use the current cd(4) driver with some modifications to that driver. The problem with RAID devices is that each RAID card has a different interface, so it really wouldn't make sense to hack CAM to work with each new RAID card. Mike's idea of doing a block driver for normal array access and then passthrough for other devices is likely the right way to go. > > 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 don't think so. Ken -- Kenneth Merry ken@kdm.org To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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