Date: Wed, 30 Jan 2002 21:12:56 -0500 From: Brian T.Schellenberger <bts@babbleon.org> To: "Kevin Oberman" <oberman@es.net> Cc: Varshavchick Alexander <alex@metrocom.ru>, questions@FreeBSD.ORG, hackers@freebsd.org Subject: Re: Again Softupdates on 4.5 Message-ID: <20020131021257.193F44078@i8k.babbleon.org> In-Reply-To: <20020130193145.5ED395D0B@ptavv.es.net> References: <20020130193145.5ED395D0B@ptavv.es.net>
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On Wednesday 30 January 2002 02:31 pm, Kevin Oberman wrote:
> > From: Brian T.Schellenberger <bts@babbleon.org>
> > Date: Wed, 30 Jan 2002 14:17:27 -0500
> >
> > On Wednesday 30 January 2002 12:53 pm, Kevin Oberman wrote:
> > > > Date: Wed, 30 Jan 2002 20:09:14 +0300 (MSK)
> > > > From: Varshavchick Alexander <alex@metrocom.ru>
> > > > Sender: owner-freebsd-questions@FreeBSD.ORG
> > > >
> > > > Then the difference lays only in the fact that on 4.5 the softupdates
> > > > flag can be turned on in the sysinstall procedure?
> > >
> > > No. I means that sysinstall turns on softupdates for all non-root,
> > > non-swap partitions by default. Under 4.4 you had to tell sysinstall
> > > that you wanted softupdates (with the 'S' command). There is no change
> > > to the functionality in 4.5, only to the default operation.
> >
> > Does 4.5 also leave write-caching on by default? If so, I think that's a
> > terrible mistake. Would I be correct in assuming it's way to late to get
> > this reconsidered?
>
> Yes, write-cache is enabled by default on 4.5 (as it was on 4.4).
>
> The debate on this has been long and often mis-informed. There is a
> real risk of metadata corruption with write caching and softupdates,
> but it appears to be EXTREMELY small. So far no case of it has
> actually been confirmed. There is a significant chance of data loss in
> recently updated files with write-cache, but that is also true without
> softupdates. The only totally safe way to deal with this is to run fully
> synchronous with write-cache disabled.
My experience is that combining the two of them greatly magnifies the risk of
losing recent updates, and that in fact data can be lost even without any
system crash or other problems when using them together. Indeed, I have a
very reproducable case of this on my system--
If I enabled softupdates + write cache and then I do
cd /some-big-directory
rm -r *
shutdown -p now
then the file system will be corrupted on reboot.
I find this as default behavior pretty ridiculous, and it it comes about
*only* as result of having both enabled together.
>
> As I understand it the conclusion of the core team was that
> softupdates advantages more than justified the risks. 4.5 has been
> released. I already have burned CDs. I think it's too late.
>
> > (And what list ought I have been reading to have known about these
> > plans?)
>
> hackers and stable.
>
> R. Kevin Oberman, Network Engineer
> Energy Sciences Network (ESnet)
> Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
> E-mail: oberman@es.net Phone: +1 510 486-8634
--
Brian T. Schellenberger . . . . . . . bts@wnt.sas.com (work)
Brian, the man from Babble-On . . . . bts@babbleon.org (personal)
ME --> http://www.babbleon.org
http://www.eff.org <-- GOOD GUYS --> http://www.programming-freedom.org
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