Date: Fri, 31 Jan 1997 13:07:17 -0800 (PST) From: Simon Shapiro <Shimon@i-Connect.Net> To: Peter Dufault <dufault@hda.com> Cc: freebsd-scsi@freebsd.org, julian@whistle.com Subject: Re: NewComer Questions... Message-ID: <XFMail.970131133216.Shimon@i-Connect.Net> In-Reply-To: <199701311054.FAA12508@hda.hda.com>
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Hi Peter Dufault; On 31-Jan-97 you wrote: ... Some good news delted... > I use a shared SCSI bus between two systems for debugging (again, > with 1542s; build using a fast system that stays up and reboot the > slow system) as you plan on doing and that works fine as long as > you stay on your toes and don't do anything stupid with multiply > mounted file systems. All the work will be done on raw devices, or r/o file systems. > Are you using the SCSI disk block range reservation in your DLM? I > thought about doing that but decided it was too likely to uncover > bugs in drive firmware and never even tried it. Thisd is an interesting idea. much like you, I put it in the category of synchronized spindles, RAID-3 and such; It is in the brochre, probably in the specs., maybe even in the firmware. Do I want to debug it? Probably not :-) Te DLM is implemented very generically and handles ALL the sharing issues. All that is expected of the SCSI system is to tolerate each other's initiator. The ``disk'' access will be done through something like ccd that will virtualize the disks and will be the one with the ``saring awareness''. We want the SCSI part to be as plain as possible. We want the code compartmentalized as much as possible. This enhances the amount/depth of the code that will be pumped back into the public domain. My employer pays for all of this... ... > I assume you do this over ethernet and not processor send/receive? Of course. Maybe even RS-232. Don't jump... :-)) ... > The field for units in the minor number is only 5 bits. The > dkunit stuff has a lower limit I think, but that affects only > disk statistics. We may need to visit these. Later. > No interrupts, no sleeping. The kernel memory is there and you can > malloc etc, but I'm not sure what you mean about VM totally functional. Exactly that. you can use virtual addresses, malloc is alive, etc. Interesting you say no interrupts because some SCSI adapters use splbio there... Simon
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