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Date: Thu, 30 Oct 2008 22:05:43 -0500
From: Rich Winkel <rich@math.missouri.edu>
To: Jeremy Chadwick <koitsu@freebsd.org>
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Cc: Rich Winkel <rich@math.missouri.edu>, freebsd-questions@freebsd.org
Subject: Re: Filesystem, RAID Question
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On Thu, Oct 30, 2008 at 07:33:47PM -0700, Jeremy Chadwick wrote:
> > One of the main functions of softupdates is to order disk updates in such
> > a way that the fs organizational integrity is maintained at all times.
> 
> And we've recently found that this is simply not the case.  The benefits
> of SU are applicable to very specific environments; desktop PCs are the
> main ones, offering great performance improvements there.

Thanks for pointing that out.  Is this an acknowledged bug in SU?  Is it
still a problem in 7.0?

> > Of course this doesn't protect against actual sector corruption, but if
> > the disk is between writes at the time it loses power, the fs structure
> > is supposed to still be internally consistent.  At least that's my
> > understanding of it.
> 
> Yep, that's how I understand it as well.  But this is a different topic
> than what we were discussing 2-3 replies ago, talking about how a RAID
> controller with cache + BBU is sufficient enough to guarantee data
> integrity even when power is lost -- that's incorrect.

The reason I brought it up is that it occurred to me that if the hardware
raid card reorders disk i/o it would mess with SU's ordering.  I wonder
whether this was happening in the previous thread you referred to
concerning fsck?

Rich