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From: rbj@icst-cmr.arpa
Newsgroups: comp.unix.wizards
Subject: File system placement
Message-ID: <7651@brl-adm.ARPA>
Date: Tue, 2-Jun-87 15:13:13 EDT
Article-I.D.: brl-adm.7651
Posted: Tue Jun  2 15:13:13 1987
Date-Received: Thu, 4-Jun-87 06:41:27 EDT
Sender: news@brl-adm.ARPA
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   Well, actually, some people have shifted the 'a' and 'b' partitions to
   the middle of the disk for precisely this reason.  On Sequent Computers,
   drives on their new dual channel disk controller (eagles and swallows)
   have partitions laid out as follows (not to scale):

    ---------------------------------------------------------------------------
   |               h               |a|   b   |               g               |
    ---------------------------------------------------------------------------
   |               d                    |                    e               |
    ---------------------------------------------------------------------------
   |                                    c                                    |
    ---------------------------------------------------------------------------

   i.e., you can run partitions h,a,b & g or d & e or just c.  I've found this
   partition layout to be doublely advantageous in that your 'user-files only'
   disks don't need to have wasted tiny 'a' & 'b' partitions on them.

   If you want to change the partition sizes yourself on whatever system you
   have, it's not too difficult if you have source.  Just modify the tables in
   the driver and in /etc/disktab (the latter so newfs knows what you did).

   --Brian
   {seismo,allegra,ihnp4}!scgvaxd!brian

Source is not necessary. The name of the partition tables in 4BSD is
DISK_sizes, where DISK is replaced by whatever you have. In DYNIX, it
is singular. Try `strings /*nix | grep _size' and look for things like
`eagle_size, rm03_sizes, cdc####_sizes, etc. The tables are an array of
eight structures of two ints apiece. The first int is the number of
sectors and the second is the starting *cylinder*.

ADB works quite well under 4BSD and DDT works nicely under DYNIX, altho
you have to invoke the latter twice, once for the running system and
once for the one on disk. You can do this while the system is running
as long as you don't change things too radically.

One last thing. I always boost the kernel's idea of the `a' partition
to overlap the `b' partition as well. That way I can make a combination
file system using the -s option on newfs.

	(Root Boy) Jim Cottrell	<rbj@icst-cmr.arpa>
	National Bureau of Standards
	Flamer's Hotline: (301) 975-5688
Does someone from PEORIA have a SHORTER ATTENTION span than me?