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Date:      Sat, 18 Mar 1995 17:30:28 +1000
From:      Bruce Evans <bde@zeta.org.au>
To:        bde@zeta.org.au, terry@cs.weber.edu
Cc:        current@FreeBSD.org, phk@ref.tfs.com, rgrimes@gndrsh.aac.dev.com, wollman@halloran-eldar.lcs.mit.edu
Subject:   Re: newfs: sectors per cylinder (4096) disagrees with disk label (36)
Message-ID:  <199503180730.RAA11965@godzilla.zeta.org.au>

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>> 2^24 is plenty of devices!  Naming them right is harder.  I once
>> had MAKEDEV generating about 700 disk devices but have reduced that
>> to about 200 (27 per unit) by only generating partitions for the
>> first BSD partition.  This required naming the first BSD partition
>> canonically.  I don't really like this - it's like renumbering
>> SCSI devices.

>OK, I guess I was getting ahead of myself by assuming a linearly
>expanding Nd matrix with direct bit assignments.

Slices _are_ numbered orthogonally, except slice 0 is an alias for
the first BSD slice (s1..s30) and slice 1 partition c is an alias
for the whole disk.  Slice names may be locked into fstab by not
using the aliases (except there is no canonical way of numbering
extended DOSpartitions).

>I'd steal fully half of the available bits for single instance
>devices like "the controller" and "the whole drive".

Maybe I should have done that.  The special slices 0 and 1 are messy
to support.

>I think your device creation problems get solved by cloning and use
>of a devfs exposed as a /dev in the file system name space.

Yes, I hope we have devfs before the current scheme runs out of bits.

>/dev/scsi/controller/target[/lun][/DOS_PARTITION][/BSD_SLICE]

I find even rsd0s2a to hard to type compared with rsd0a :-).

Bruce



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