Subject: Re: Another changer, another changer problem
To: None <>
From: Greg A. Woods <>
List: current-users
Date: 10/07/1998 17:23:16
[ On Wed, October 7, 1998 at 15:31:52 (+0930), Brett Lymn wrote: ]
> Subject: Re: Another changer, another changer problem
> According to Greg A. Woods:
> >
> >Perhaps you're not thinking of *real* machines.  Certainly with PCs you
> >are likely to be correct, but with all *real* machines that I've ever
> >dealt with you can easily find "c2".
> Not sure what you mean by a "real" machine here ;-).  I would defy you
> to pick c2 on a Sun after a few adds & removes of hardware with doing
> a "boot -r" in between.

Again, I'm most definitely *not* referring to Solaris.  I'm talking
only about the hardware itself.

> >Seriously though, maybe a pure cNtNdN scheme isn't good enough for
> >NetBSD.  Maybe it's better to stick to driver prefixes, but be more
> >explicit about it -- i.e. don't lump all SCSI controllers into sd and
> >st, and so on, but actually use espNtNlN and so on.
> 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).

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.

							Greg A. Woods

+1 416 218-0098      VE3TCP      <>      <robohack!woods>
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