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Date: Sun, 28 Aug 2011 08:36:56 -0600 (MDT)
From: Warren Block <wblock@wonkity.com>
To: Polytropon <freebsd@edvax.de>
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	(wonkity.com [127.0.0.1]); Sun, 28 Aug 2011 08:36:56 -0600 (MDT)
Cc: FreeBSD Questions <freebsd-questions@freebsd.org>
Subject: Re: Identifying disk activity
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On Sun, 28 Aug 2011, Polytropon wrote:

>>> Is there a way to force "synchronous disk activity"?
>>
>> Turning off soft updates will help, but not make disk writes
>> totally synchronous.
>
> Can this be done easily (e. g. "tunefs -n disable <devices" in
> SUM to the unmounted partitions), without data loss? I have to
> admit that I've never tried that before.

SUM isn't needed, just have the filesystem unmounted.  Never had data 
loss from it.

Disabling write caching will also help to make filesystem writes more 
synchronous.  There are several sysctls and some information on soft 
updates at http://www.freebsd.org/doc/handbook/configtuning-disk.html.