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From: kjb@cs.vu.nl (Kees J Bot)
Subject: Re: FS size supported in 1.7
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References: <DJzBDs.4J7@bercos.de> <DJzzp7.EIt.0.-s@cs.vu.nl> <DK1JEA.A41@bercos.de> <DK33sn.8xz.0.-s@cs.vu.nl> <4bjd8l$hpu@klaava.helsinki.fi>
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Organization: Fac. Wiskunde & Informatica, VU, Amsterdam
Date: Sun, 24 Dec 1995 15:38:48 GMT
Message-ID: <DK3Kso.I1B.0.-s@cs.vu.nl>
Lines: 43

torvalds@cc.Helsinki.FI (Linus Torvalds) writes:
>
>In article <DK33sn.8xz.0.-s@cs.vu.nl>, Kees J Bot <kjb@cs.vu.nl> wrote:
>>
>>The disk drivers use a 32-bit block number even under Minix 1.5.  So the
>>size of the disk or a partition is limited to 4 G as far as the drivers
>>are concerned.
>
>Actually, in this day of multi-GB harddisks, it might be worth pointing
>out that 32-bit block numbers are good for 4TB worth of disk-space, as
>long as you do block-addressing (assuming a 1kB block size here).  This
>is how the linux ext2fs is able to handle large (where large means ">>
>4GB", not "> 256MB" ;-) filesystems even though all block numbers are 32
>bit. 

Oops, I should have written "32 bit disk offsets".  The interface to the
disk is <byte position, byte length> under Minix.  FS knows nothing about
the disk block size, except that that reading or writing 1 kB blocks is
OK.  This is all very nice and simple, but with big disks becoming
dirt cheap we have yet another limit for Minix to bump in to.  (But only
if one wants to put Minix at the end of the disk.)

I already have a fix though, Minix-vmd has 64 bit disk positions thanks
to a dozen assembly functions (add64(), mul64(), etc.).  It also only
loads bit map blocks when needed, and only checks file systems that were
active at the time of a crash.  If the pressure becomes big enough I
will put those features into standard Minix.

Not that I think it will be necessary, after all, people only use Minix
to turn old XT's into terminals for Linux.  :-)

Do we always talk about file systems around Xmas, Linus?  Three years ago
around this time I explained the Minix V2 file system to you.  You were
thinking about implementing V2 as a stable default file system when the
old extfs was still undependable.  Shortly after extfs became much
better, allowing you to forget about Minix V2.

(My mail archive tells me that the first message in the email exchange
on V2 was dated "Thu, 24 Dec 92 03:16:16 +0200", exactly the same day
three years ago.  I hate these unexplainable coincidences.)
--
	                        Kees J. Bot  (kjb@cs.vu.nl)
	              Systems Programmer, Vrije Universiteit Amsterdam
