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From: chris@umcp-cs.UUCP (Chris Torek)
Newsgroups: net.unix-wizards
Subject: Re: Location of partition table on disk
Message-ID: <3771@umcp-cs.UUCP>
Date: Thu, 9-Oct-86 07:51:25 EDT
Article-I.D.: umcp-cs.3771
Posted: Thu Oct  9 07:51:25 1986
Date-Received: Fri, 10-Oct-86 01:28:52 EDT
References: <7473@sun.uucp> <15583@mordor.ARPA> <1173@hoptoad.uucp> <7195@utzoo.UUCP>
Reply-To: chris@umcp-cs.UUCP (Chris Torek)
Organization: University of Maryland, Dept. of Computer Sci.
Lines: 35

In article <7195@utzoo.UUCP> henry@utzoo.UUCP (Henry Spencer) writes:
>I too thought it would be a good idea to have the partition table
>on the disk it partitioned, until I read a paper on the Cray-2 Unix
>port. ... the size and disk location of each partition is recorded
>in the /dev inode for it. ... It seems to me that this is a cleaner
>solution all around.

I remain unconvinced.  It is certainly an intriguing idea, and not
entirely without precedent (we have a local kernel hack that already
puts things into the disk block fields of /dev inodes).  It has some
definite advantages:

	- the number of partitions per drive is not fixed;
	- one can record striping information cleanly;
	- it takes very little driver code.

It also has some definite disadvantages:

	- the number of partitions per drive is not fixed;
	- there is a bootstrap problem (avoided by compiling
	  in the root partition info);
	- it does little for removable packs (indeed, it is
	  quite possibly harmful in such cases);
	- it discourages sharing the information among operating
	  systems (VMS to read Unix /dev directories anyone?).

I still believe that the disk layout is a property of the disk
pack, not of the file systems mounted thereon.  There is certainly
some crossover, though.  Perhaps the information should be in
several places, and cross-verified---though that brings up the
question of what to do if the verification fails. . . .
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 1516)
UUCP:	seismo!umcp-cs!chris
CSNet:	chris@umcp-cs		ARPA:	chris@mimsy.umd.edu