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Date: Sun, 22 Feb 2004 17:49:46 +0000
From: Heinrich Rebehn <rebehn@ant.uni-bremen.de>
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cc: questions@freebsd.org
Subject: Re: UNEXPECTED SOFTUPDATES INCONSISTENCY
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Gabriel Ambuehl wrote:
> Hello Heinrich,
> 
> Sunday, February 22, 2004, 5:00:27 PM, you wrote:
> 
>>Why that? I can imagine that i lose data in case of a power failure, but
>>why in case of a crash?
> 
> 
> Well I guess the card COULD still commit the data, however, who knows
> if it actually does it?
> 
> 
>>And why is write cache only dangerous with softupdates, as you wrote above?
> 
> 
> IIRC softupdates relies on the assumption that when the softupdate
> changes return, they really ARE on the disk. It's the same with most
> RDBMS: because they go to great lengths to ensure the journal is in an
> ok state they need to know for sure that the data they wrote to it
> actually made it to disk.
> 
> 
>>Since i found no word about disabling write cache in the FreeBSD
>>handbook or in man tuning(7), i would really like to know, if this is
>>just a rumour, or where does it come from?
> 
> 
> I can't say for sure, but I have little confidence in write caching
> anyhow. It changes semantics the system relies on, for one.
> 
> 
> 
> 
> Best regards,
>  Gabriel
> 
Gabriel,
what you write does make sense, although i really can't understand why 
this important info is not in the FreeBSD documentation.
I have disabled write cache, but i will keep softupdates disabled as 
well for now, and see how the system behaves.

Thanks for your help,

	Heinrich