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SubjectRe: devfs
  From: Bob Tracy <rct@gherkin.sa.wlk.com>
Date: Wed, 14 Jan 1998 07:29:40 -0600 (CST)

Time to lay it to rest, but here's a way for folks to live with 'd'
and 's'. Think 'd == device, s == subdevice' and assign whatever
meaning is consistent for a particular type of device. In the
System III/V way of naming things, 'd' was never intended to represent
'disk'. The original meaning of 's' is a bit more obscure, and 'slice'
was at least as common an interpretation as 'subdevice' as I remember
it. Regardless, 'stripe' or 'strip' wasn't one of the valid meanings.
In my mind at least, there's a natural correlation between a
subdevice and a partition, and 's' isn't as limited as 'p' if/when
you want to apply the naming scheme to a device that doesn't have
partitions.

An example: for SCSI devices, '(d)evice == LUN'.

One more example: ESDI disks. On the old 3B2 computers with ESDI
disks, a SCSI target ID (t1-t7, t0 was reserved for the host adapter)
corresponded to a SCSI <--> ESDI controller (Everex) that could
support up to four spindles (d0-d3). Simple math implies you could
hang up to 28 spindles off a single SCSI host adapter if you were
crazy enough to put up with the I/O bottleneck.

The ESDI example in particular is why I would prefer 'd' to 'u', but
I can live with 'u' if that's the consensus.

The device/subdevice explanation makes a great deal of sense, and would allow
extending the naming consistently to non-SCSI devices where the use of logical
unit and slice isn't appropriate. If it's not yet too late, I think this is a
good argument for using "d" and "s".

Leonard

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