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From: jerry@oliveb.UUCP (Jerry F Aguirre)
Newsgroups: comp.unix.wizards
Subject: Re: File system placement
Message-ID: <1618@oliveb.UUCP>
Date: Thu, 25-Jun-87 18:22:12 EDT
Article-I.D.: oliveb.1618
Posted: Thu Jun 25 18:22:12 1987
Date-Received: Sat, 27-Jun-87 04:10:59 EDT
References: <1294@qfdts.OZ> <755@scgvaxd.UUCP> <783@mcgill-vision.UUCP>
Reply-To: jerry@oliveb.UUCP (Jerry F Aguirre)
Organization: Olivetti ATC; Cupertino, Ca
Lines: 26

Regarding putting the root and swap in the middle of the disk to reduce
seek time.  Back in our PDP/11 days we used to run that way.  Our disk
layout looked like:

	|   /usr      |root|swap|    /u1   |

The bootstrap at sector zero was unchanged, /boot was moved to
/usr/boot and modified to use the new partitions.

In normal usage everything booted and ran fine.  Manual booting required
typing in "hp(0,magic_number)unix" where magic_number was to offset to
the root partition.  I suppose an alternative would be to duplicate the
kernal on / and /usr.  You could then boot from the first partition but
the kernal would still make the middle partition the root.  This could
get confusing if you updated one but not the other.

This was a real advantage on the PDP11 because forks were implemented
using a swap.  The typical process would execute from /bin and then get
swapped, lots of IO to the root and swap.

If your application is disk intensive then a root and swap in the middle
configuration would probably be worth it.  Of course adding more memory
and buffers will reduce both root access and swapping.  I suggest that
you do some measurements before going thru the extra hassle.

					Jerry Aguirre