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Date:      Thu, 3 Aug 2000 15:20:02 -0700 (PDT)
From:      Tom <tom@uniserve.com>
To:        Peter Jeremy <peter.jeremy@alcatel.com.au>
Cc:        Paul Coyne <pac@geodesic.com>, freebsd-stable@FreeBSD.ORG
Subject:   Re: Cached versus non cached disk I/O
Message-ID:  <Pine.BSF.4.05.10008031517100.12192-100000@shell.uniserve.ca>
In-Reply-To: <00Aug4.072549est.115835@border.alcanet.com.au>

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On Fri, 4 Aug 2000, Peter Jeremy wrote:

> On Tue, Jul 11, 2000 at 09:06:31PM -0700, Tom wrote:
> >  It
> >should be obvious that write-buffering metadata can cause problems, even
> >with softupdates, though softupdates is clearly better than async.
> 
> Not quite.  softupdates is actually more robust than a normal FS
> mount (and far more robust than async).  The softupdates code
> controls the ordering of both data and metadata writes to ensure
> that the FS on disk is always internally consistent.  With a
> normal mount, the metadata is mostly internally consistent, but
> is not necessarily consistent with the data.

  Not likely.  I personally pushed softupdates over the edge before (see
archives).  In my case, the amount of unwritten metadata filled up all
kernel space.  The filesystem was recoverable, but fsck filled up
lost+found several times (that should be considered a fsck bug that wasn't
possible to expose without softupdates). It was rather messy.

> Peter


Tom
Uniserve



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