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Date:      Sun, 17 Jan 1999 13:09:41 -0500 (EST)
From:      Alfred Perlstein <bright@hotjobs.com>
To:        Christian Kuhtz <ck@adsu.bellsouth.com>
Cc:        freebsd-current@FreeBSD.ORG
Subject:   Re: ufs async
Message-ID:  <Pine.BSF.4.05.9901171302350.76427-100000@bright.fx.genx.net>
In-Reply-To: <19990117112925.A19618@oreo.adsu.bellsouth.com>

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On Sun, 17 Jan 1999, Christian Kuhtz wrote:

> 
> Hey gang:
> 
> Somebody mentioned the other day that UFS async isn't entirely async, and
> that directories are (always) sync.  Is that true?

not afaik.

> Can somebody elaborate on why that is?

normal UFS mounts are async in respect to data, however
meta-data/directory-ops are done sync so that your filesystem doesn't
resemble the aftermath of "squril VS 18-wheeler" in the case of a power
outage/crash

you CAN mount UFS totally async, but then if you incorrectly shutdown your
box prepare to recreate the filesystem (*)

in 3.0 you have the option of 'softupdates' if you qualify for the
license, look in the /usr/src/contrib/sys/softupdates/README for an
explanation.

softupdates allow for safe async because writes to the meta-data are
ordered in a failsafe manner.

-Alfred

(*) i used to mount async for builds and compiling at times a while back,
i never had massive destruction, but you never know, i suspect renaming
your /usr and hitting the reset button would be considered fatal if timed
properly

> 
> Cheers,
> Chris
> 
> -- 
>   "We are not bound by any concept, we are just bound to make any concept work 
>    better than others."                                  --  Dr. Ferry Porsche
> 
> [Disclaimer: I speak for myself and my views are my own and not in any way to
>              be construed as the views of BellSouth Corporation. ]
> 
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