Date: Mon, 29 Aug 2005 17:15:39 -0400 From: Chuck Swiger <cswiger@mac.com> To: Matthias Buelow <mkb@incubus.de> Cc: freebsd-stable@freebsd.org Subject: Re: Sysinstall automatic filesystem size generation. Message-ID: <43137AFB.9060304@mac.com> In-Reply-To: <20050829204714.GC1462@drjekyll.mkbuelow.net> References: <20050829120415.GA1462@drjekyll.mkbuelow.net> <200508291836.j7TIaVEk013147@gw.catspoiler.org> <20050829185933.GB1462@drjekyll.mkbuelow.net> <431362ED.9030800@mac.com> <20050829204714.GC1462@drjekyll.mkbuelow.net>
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Matthias Buelow wrote:
> Chuck Swiger wrote:
>>PS: Haven't we had this conversation before?
>
> Yes, indeed, and I don't want to reopen that issue since that would
> lead to no new insights (and since I don't have the time atm. to
> contribute anything I couldn't provide any stuff myself).
Yet you seem willing to spend time discussing the matter...?
> I was just refuting the claim of "very robust" filesystem when power goes
> out in the context of 200GB consumer-grade hardware that this thread
> was talking about.
Most of the time, a FreeBSD system will come back up without losing data older
than about thirty seconds, and that is tunable. Have you even tried to change
the syncer sysctls I mentioned?
> I think until a satisfactory solution can be
> found (by making softupdates and/or a journalled filesystem as
> reliable as possible through mechanisms like write-request barriers
> and appropriate flushing at these) users who're running FreeBSD on
> end-consumer hardware (desktop PC as workstation or personal server)
> should be warned that softupdates does NOT work as described on
> their hardware and that the filesystem can easily be corrupted when
> the power goes out, no matter if softupdates is enabled or not.
Great. I think "man ata" already says exactly this:
hw.ata.wc
set to 1 to enable Write Caching, 0 to disable (default is enabled).
WARNING: can cause data loss on power failures.
If your hard drive no longer works correctly when write-caching is disabled,
it's defective. Nothing FreeBSD or any other system can do is going to change
that.
> One often sees the "softupdates" argument being fielded by FreeBSD
> advocates, typically against Linux users with journalled fs, on web
> forums, usenet and other less authoritative (and knowledgable)
> places of discussion, and it is often presented as if it were some
> kind of magic bullet that makes filesystem corruption impossible.
"Often?" Strawman test: can you point out 3 examples by message-id or URL?
And if you prefer to run a journalled filesystem under Linux instead of
softupdates under FreeBSD, by all means, do whatever makes you happy.
> This simply is not so.
Very good.
--
-Chuck
PS: I don't want a thread to end on a negative note. It would be useful if
FreeBSD had a more adaptable method for dealing with drive power management and
caching; in particular, for laptops it might be nice to cache data for much
longer-- perhaps even hours-- if nothing fsync()s, in order to permit the drive
to spin down.
(This is something both Windows and MacOS X are learning to do pretty well.)
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