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From: mbr@aoa.UUCP (Mark Rosenthal)
Newsgroups: comp.unix.wizards
Subject: Re: request for help in repartitioning RA81 disk
Message-ID: <556@aoa.UUCP>
Date: Wed, 25-Nov-87 12:25:29 EST
Article-I.D.: aoa.556
Posted: Wed Nov 25 12:25:29 1987
Date-Received: Sun, 29-Nov-87 08:49:06 EST
References: <13086@comp.vuw.ac.nz>
Reply-To: mbr@aoa.UUCP (Mark Rosenthal)
Organization: Adaptive Optics Assoc., Cambridge, Mass. USA
Lines: 44

In article <13086@comp.vuw.ac.nz> edward@comp.vuw.ac.nz (Ed Wilkinson) writes:
>We're about to install Ultrix 2.0 & are taking the time  to  con-
>sider  repartitioning our disk.
	.
	.
	.
>If  we  did  have
>these  2  partitions, we might have to use chpt - I've heard that
>having non-standard partitions is not a good idea. Is that right?
>If so, why? BTW, our disk is an RA81 on a Vax 750.

I installed Ultrix 2.0 on our 8650 last July.  The partitioning was one of
the most annoying problems.  I already had non-standard partition sizes on
drive 0, which I was using with Ultrix 1.2.  However, the installation script
insisted on overwriting these with the standard partition sizes.  I was able
to re-create my old non-standard partition sizes, but it required a lot of
shuffling things back and forth between disks.  I allowed the installation
script to do its thing, and create a system on drive 0 with standard size
partitions.  I used this system to create a minimal system on drive 1.  This
allowed me to boot a system from drive 1 which did not depend on anything on
drive 0.  (Actually, this took a few tries because I forgot to change the
config file to make the kernel swap on drive 1.  Oops.)  Having done this,
I could use chpt to change partitions on drive 0 and not have to worry about
depending on data coming from partitions of the disk I was trying to
repartition.  After this, I restored drive 0 from backup tapes.

A related problem is the fact that chpt will allow you to increase the size of
the 'a' partition, but will not allow you to decrease it.  Nowhere could I
find this documented.  And the error message is (I don't remember exactly;
it's been a while) something like "invalid partition size", which did not
necessarily lead me to suspect that there is a special restriction on how
you can change partition sizes on drive 'a'.  Once I had this explained to me
by the people at the Ultrix support line, I came up with a kludge which gets
around this.  Write a small C program which outputs 1K bytes of zeroes and run
it with standard output redirected to the partition 'a' of the raw disk device,
e.g. /dev/rra1a.  This will clobber the partition table on the disk.  The next
time you run chpt, it will think it is looking at an uninitialized disk, and
will happily change the partition sizes to anything which will fit on the disk.
-- 
	Mark of the Valley of Roses
	...!{harvard,ima}!bbn!aoa!mbr