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From: brian@scgvaxd.UUCP
Newsgroups: comp.unix.wizards
Subject: Re: File system placement
Message-ID: <755@scgvaxd.UUCP>
Date: Thu, 21-May-87 19:40:46 EDT
Article-I.D.: scgvaxd.755
Posted: Thu May 21 19:40:46 1987
Date-Received: Sat, 23-May-87 08:19:06 EDT
References: <1294@qfdts.OZ>
Reply-To: brian@scgvaxd.UUCP (Brian D. Zill)
Organization: Hughes Aircraft Co., El Segundo, CA
Lines: 42
Keywords: location of key file systems for optimal access
Summary: it's been done

In article <1294@qfdts.OZ> phil@qfdts.OZ (Phil Chadwick) writes:
>On the day I first booted UNIX from release tape, root, swap,
>tmp and usr were placed on the disk starting at cylinder 0.
>
>For optimal average access time, important file systems should
>reside in the mid-range cylinders of a disk.  So why are our
>disks still arranged with the most important (and subjectively,
>the heaviest) access biased around the lowest cylinder numbers?
>
>I am giving serious consideration to rearranging the larger
>disks (say those > 300Mb) with root, tmp, swap and usr (not
>including users' files) fair bang in the middle.
>
>Any comments?

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).

On a related performance issue, if you have three or more disks, you should
also put root, tmp, and usr on separate disks.  And have multiple swap areas.

					--Brian

{seismo,allegra,ihnp4}!scgvaxd!brian