Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!uunet!mcsun!ukc!icdoc!qmw-cs!liam
From: liam@cs.qmw.ac.uk (William Roberts)
Newsgroups: comp.unix.aux
Subject: Re: Help with A/UX 1.1 on 3rd Party drive
Keywords: A/UX 1.1 X11R4 3rd Party Drives
Message-ID: <2349@sequent.cs.qmw.ac.uk>
Date: 7 Jun 90 20:47:26 GMT
References: <167@cis9.INGR.COM> <2337@sequent.cs.qmw.ac.uk> <1990Jun7.030853.22479@portia.Stanford.EDU>
Organization: Computer Science Dept, QMW, University of London, UK.
Lines: 40

In <1990Jun7.030853.22479@portia.Stanford.EDU> name@portiaStanford.EDU (tony cooper) writes:

>It seems doubtful that swap space is overflowing ...

I repeat, it is DEFINITELY NOT SWAP that is overwriting other
parts of the disk unless the partitions defined in the
partition map actually overlap.

The pname'ing of a disk partition (which happens automatically
for swap) is effectively initialising a translation function
from sectors requested of that particular A/UX device (in this
case 24,1) and physical sector requests over the SCSI bus.
There is range checking, and silly values are ignored: for
example

        dd if=/dev/dsk/c0d0s1 of=/dev/null

will stop after the number of blocks defined to be in the swap
partition according to the partition map, as will the (probably
lethal)

        dd if=/dev/dsk/c0d0s0 of=/dev/dsk/c0d0s1

[[ Remember children - don't try this at home* ]]

The value of SWAPCNT that is kconfig'd into the kernel does not
matter: if it is too small then not all of swap will be used,
if it is too big then when you exceed the size that the
partition map allows you will get "process killed due to i/o
error in swap" messages from the kernel.


-------------
* Or if you do, remember to do it single-user and wear a condom.
-- 

William Roberts                 ARPA: liam@cs.qmw.ac.uk
Queen Mary & Westfield College  UUCP: liam@qmw-cs.UUCP
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