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Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!cbmvax!jesup
From: jesup@cbmvax.commodore.com (Randell Jesup)
Newsgroups: comp.sys.amiga,comp.sys.amiga.tech
Subject: Re: I hate AmigaDos file systems (was Re: HD Errors
Message-ID: <17156@cbmvax.commodore.com>
Date: 7 Jan 91 03:16:45 GMT
References: <7455@sugar.hackercorp.com> <1991Jan4.191249.14442@jato.jpl <37583@cup.portal.com> <1991Jan5.233130.24022@lavaca.uh.edu>
Reply-To: jesup@cbmvax.commodore.com (Randell Jesup)
Organization: Commodore, West Chester, PA
Lines: 32

In article <1991Jan5.233130.24022@lavaca.uh.edu> jet@karazm.math.uh.edu ("J. Eric Townsend") writes:
>Why is the FS so fragile compared to other micros? I haven't looked too
>closely at AmigaDos (don't even own the RKMs, etc..), but it seems that
>*somebody* out there will know the answer to this question.

	FFS is slightly more fragile than OFS (but only in that recovery
programs can't recover files that have lost their header block or an
extension block).  Of course, this helps it be 5-10 times faster too.

	I suspect (I don't know the MSDOS filesystem well) that MSDOS
merely ignores the fact that the filesystem was unstable.  I suspect if
it's writing to the FAT when you reboot, you're really hosed.  In other cases,
the file being written may be garbage or have an unreadable sector in it.

	The Amiga FS knows when the FS is unstable state, so it tries to
figure out what the stable state is by scanning the directory tree to build
a new allocation bitmap.  If a fileheader or exxtension block was hit by
the power-down, it won't be able to rebuild it.

	Before 2.0, the FS was somewhat vulnerable to something tromping
on it's memory and making it think blocks were free that weren't.  This is less
likely under 2.0, since the bitmap is no longer cached in memory, it's read
from disk as needed.  In reality, I doubt most FS problems result from programs
trashing the bitmap (trashing that wild usually kills the system fast), but
it can happen.  Steve Beats may answer with more detailed info.

-- 
Randell Jesup, Keeper of AmigaDos, Commodore Engineering.
{uunet|rutgers}!cbmvax!jesup, jesup@cbmvax.commodore.com  BIX: rjesup  
The compiler runs
Like a swift-flowing river
I wait in silence.  (From "The Zen of Programming")  ;-)