linux-kernel - Re: New filesystem for Linux

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Date:	Mon, 06 Nov 2006 01:36:09 +0100
From:	Rene Herman <rene.herman@...access.nl>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Kyle Moffett <mrmacman_g4@....com>,
	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>,
	Albert Cahalan <acahalan@...il.com>, kangur@...com.net,
	linux-kernel@...r.kernel.org
Subject: Re: New filesystem for Linux

H. Peter Anvin wrote:

> Rene Herman wrote:

>> For primary (and extended) partitions, yes. I haven't used any version 
>> of DOS that has ever objected to arbitrarily aligned partitions in the 
>> MBR (and I do align them arbitrarily since I always make my partitions 
>> some exact size and start the next partition in the next sector).
>>
>> Different though for logical partitions inside an extended. As late as 
>> Windows 98, DOS would object to non-aligned logicals, at the very 
>> least with some settings for the BIOS use/don't use LBA or "Large" 
>> settings.
>>
>> Linux doesn't care; I've used type 0x85 instead of 0x05 for my 
>> extended partitions dus to that for years. DOS just ignores that one...
>>
> 
> DOS, or FDISK?

DOS. It was something like DOS accepting the non cylinder-aligned 
logical but then proceding as if it were cylinder aligned anyway, 
rounding the starting sector down. This obviously is not good.

Also see the "--DOS-extended" comment in the sfdisk man page. Since I do 
remember differences when using different "Large" CHSs in the BIOS, for 
all I remember I was experiencing that problem when I ran into it. If 
so, the DOS underlying Windows 98 is among the "some versions".

In any case, yes, non-cylinder aligned logical partitions (for whichever 
defintion of "aligned" fits DOS' idea of the geometry) really do cause 
trouble.

The DR-DOS (-> Novel DOS -> Caldera OpenDOS) warning in that manpage 
seems to imply that cylinder alignment was a good idea for all 
partitions seen by it, and I do remember it being a pain in that regard 
as well. Guess it's pretty safe to not care about DR-DOS anymore though.

Rene.
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