Subject: Re: Another changer, another changer problem
To: NetBSD-current Discussion List <firstname.lastname@example.org>
From: Bill Studenmund <email@example.com>
Date: 10/07/1998 15:44:59
On Wed, 7 Oct 1998, Greg A. Woods wrote:
> [ On Wed, October 7, 1998 at 15:31:52 (+0930), Brett Lymn wrote: ]
> > Subject: Re: Another changer, another changer problem
> > How is this a benefit (seriously)? How does this make our lives
> > better? (FWIW if you have not already guessed, yes I do use Sol2 at
> > work so I am familiar with the cNtNdNsN naming).
> It's not specifically the naming convention (though that is useful for
> us humans who don't have accurate arithmetic calculators wired into our
> brains), but rather the implications of the scheme. I.e. specifically
> the implication that disks and controllers are always wired to specific
> and predicable /dev names.
> > OK, what in the real-world wants /dev/dsk/c3t10d0s2 instead of
> > /dev/sd99c? This stuff is hidden in the mount table. What
> > requirements do you have that are met by changing the device naming
> > scheme?
> The direct benefit of such a naming scheme is that it maps with a
> one-to-one correspondence on the way most people I know describe their
> hardware configurations. I never think in terms of "disk 99" I think of
> the disk set to target 3 on my fourth SCSI bus, or whatever. I have to
> look at the manual pages or source code and run 'bc' to figure out that
> it's really going to be "disk 99" (either that or actually attach it and
> reboot and then run "dmesg | more" to figure this out).
> The benefit of having disks always wired down is that they never move if
> one breaks or another is added in between (i.e. SCSI target wise).
I think the main reason that you're getting so much resistance to this
argument is that you've only wired the disks to a controller. If the
controllers re-arange themselves, then you're just as hosed as you are if
you add a disk and you're using sd*. Wiring disks to controllers is not
really wiring them down.
Any method which, right now, would wire down the controllers can just as
easily wire down disks. Today, that's editing the kernel config file.
> Auto-configuration is somewhere between good and great in certain
> cirumstances, but when it comes to critical system devices, such as
> disks, ethernet cards, ttys, etc., it can go too far too.
Then either just wire it down, or come up with some way to save
configuration state between boots.
I doubt that making a scsibus take up a whole major number will ever
happen. But some system which would be able to preserve device
configuration between boots would be interesting. And with it, the disks
could be wired down just as easily as the busses can. So sd2 could always
be at controller 3 target 5, even if controller 2 gains 20 disks.
It'd keep your disks in the same place, and I think most everyone'd be
happy w/ it.