From: cummings@hammer.Prime.COM (Kevin Cummings)
Subject: Re: extfs...what did I set myself up for?
Organization: Prime Computer R&D
Date: Fri, 31 Jul 1992 17:28:13 GMT

In article <Bs96JD.GMy@acsu.buffalo.edu>, jmsimon@acsu.buffalo.edu (JMS) writes:
> 
> Okay, question for the gurus.
> 
> I stopped testing Interactive Unix (Sun v3.0, SYSV/386v3.2) because,
> frankly, Linux 0.96c seems more stable and more usable (not to mention
> *free* with sources available ;-> ) and wiped the Interactive partition
> off my drive. 
> 
> I have a 202mb drive. My partitions are:
> 	/dev/hda1	MS-DOG	32+mb
> 	/dev/hda2	minix	30mb	/
> 	/dev/hda3	minixsw	20mb	(swap)
> 	
> 	...and now for the fun stuff...
> 
> I used efdisk to make primary partition 4 an extended partition (the
> type is 5, Extended DOS partition, I believe) encompassing the 120mb
> remaining. I then proceed to hit 'n' (new partition) and it doesn't
> prompt me for partition # any more; I proceed to finish my partition
> table as follows:
> 
> 	/dev/hda4	extdos	120mb
> 	    /dev/hda5	minix	 64mb	/usr
> 	    /dev/hda6	minix	 46mb   /home
> 	    /dev/hda7	minix	 10mb   /misc
> 
> I originally installed Linux (using the script - greast job!) only on
> /dev/hda{2,3} using a mkfs on hda2 and a mkswp on hda3. Got everything
> working, and decided to take the chance; I mkfs'ed hda{5..7}, and
> mounted them. df reports the space there, I can copy files onto them,
> create directories, umount and mount them in other places, etc.
> 
> Here's my question(s):
> 
> 	1)	Is this supposed to work? If not, will I suffer any
> 		inconceivable consequences down the road?

		Yes, this is supposed to work.  Ever since 0.95b pl2 I think.

> 	2)	Is the extended file system *just* to get partitions
> 		>64mb and longer filenames, or also for >4 partitions?

		The LINUX extended file system reportedly allows > 64MB and
		longer file system names.  You have to recompile certain
		utilities to use the new read directory routines in the
		latest version of LINUX in order to use it.

		The DOS extended partitions allow you access to more than
		the 4 primary partitions allowed by the partition table.
		(see below for a more detailed explanation.)

> Here's my basis of understanding on Linux's file system right now:
> 
> 	a)	Only 4 partitions can be used (excepting the extended
> 		filesystem, which I have heard needs a 'mkefs' command
> 		to create, and may require recompiling with a different
> 		library function to make shells and other programs "see"
> 		the directories and files within them)

When Microsoft and IBM decided on the format of the partition table in the
BOOT SECTOR of the hard disk, they limited it to 4 primary partitions.
Later on, when they realized their mistake, they added the EXTDOS partition
type so that one (or more?) of these four primary partitions could contain
more than one logical DOS disk.  These extended partitions (NOT to be confused
with the LINUX extended file system) allow up to 26 logical partitions within
them.  LINUX really doesn't care what TYPE of partition you choose to make
into a LINUX file system (or extended file system).  However, other software
that uses some of your partitions may care B^)!  I was running for a short time
with a LINUX filesystem on a SpeedStor partition, and DOS (under the SpeedStor
device driver) thought it was a valid DOS partition.  I was lucky to not have
had DOS write anything to that partition (it would have trashed the LINUX file
system on that disk I'm sure).  I'm actually surprised that the 10 MB of data
I had on it didn't confuse DOS (it would still list the directory as empty
if I ever did a DIR on it under DOS).

If you use a DOS extended partition, make sure that you use parts of it that are
NOT defined as DOS logical drives (use FDISK to make sure).  Then DOS and LINUX
should happily shared space in the same EXTDOS partition.

> 	b)	Linux 0.97 should support longer filenames and much
> 		larger partitions (on the order of terrabytes?)	

I'm not sure what Linus has in mind for his extended file systems.  There are
other file systems out there that could be ported to LINUX.  The DOS FS is
already being used in an ALPHA test state.  HPFS is a Hi Performance File System
(developed for OS/2?), FFS is a Fast File System (developed for BSD UNIX?), VFS
is a Very fast File system (FFS optimized for 386's?).  I'm pretty sure that
Linus' kernel modifications in the file system lately have been made so that it
will be easier to port new files systems onto LINUX in the future.  Each file
system defines its own parameters (filename restrictions and lengths, disk space
for the disk directory, number of disk directory entries, disk space for the data,
etc).  

I'm sure someone else will correct me if I'm wrong.

> Fantastic system, BTW. Everyone who work{s|ed} on this deserves a six-pack
> from everyone who uses it (of course, we'll never get updates and ports if
> the entire development team is swimming ;-> )

Damn, beer isn't on my new diet (sigh!).  Not until I lose another 70 pounds
anyways (about 30 or so more kilos for you continentals).

> Oh. Eventually I may look into writing a driver for my Colorado Jumbo 250
> tape backup (unless someone is already endeavoring - let me know) -- if
> anyone would like to keep me from this certain misery, an Exabyte would go
> a long way!

Yeah, I have DJ10 myself (120MB tape).  Would be nice.

=================================================================
Kevin J. Cummings                       PrimeService
20 Briarwood Road                       A Computervision Company
Framingham, Mass.                       500 Old Connecticut Path
					Framingham, Mass.
Work:  cummings@primerd.Prime.COM
Home:  cummings@kjc386.framingham.ma.us

Std. Disclaimer: "Mr. McKittrick, after careful consideration,
		  I've come to the conclusion that your new
		  defense system SUCKS..."   --  War Games
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Newsgroups: comp.os.linux