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SubjectRe: SCSI device numbering (was: Re: Ideas for v2.1
Followup to:  <>
By author: "Eric Youngdale" <>
In newsgroup:
> It would be theoretically possible to give a seperate major number
> to each different type of scsi controller. This would shift some of the
> bits to the major number, and if this were done correctly we might be able
> to make things fit in a 64 bit symmetric dev_t.
> I have seen some people argue for solutions that work for the
> small systems, but exclude the large systems. I believe that this
> is fundamentally wrong, since the problems with dynamic address
> shifting grow as the number of devices on the sysetem grow. We
> should be looking for solutions that work in the case of large
> systems (with say 500 or more disk drives), and then make sure that
> this works well for the small systems.

My experience managing large Solaris systems (which use
controller-target-LUN device naming) has led me to believe this sort
of stuff is fundamentally bogus, *especially* when there are multiple
cards involved. You will simply tend to move the stuff around too
often. The resulting problem is similar to the problem with DOS drive

My belief is that the only reasonable solution is to permit the user
to control the scanning order (including allowing gaps). The *ideal*
would be to let the user afiliate arbitrary device names which
arbitrary controller-target-LUN tuplets, but if at least the
controller scanning order is determined we're remotely OK.

I do *not* agree that the ISA/EISA/PnP/PCI bus identifier should be
encoded -- it is simply too hardware dependent.

That being said, as the Linux Device Registrar I strongly advice that
2.1 *must* be the time to increase the size of dev_t to a mininum of
32 bit; I personally advocate 64 bit with support for sparse
allocation of major numbers.


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