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Date:      Tue, 30 Aug 2005 03:11:06 +0200
From:      Matthias Buelow <mkb@incubus.de>
To:        Mark Kirkwood <markir@paradise.net.nz>
Cc:        freebsd-stable@freebsd.org
Subject:   Re: Sysinstall automatic filesystem size generation.
Message-ID:  <20050830011106.GF1462@drjekyll.mkbuelow.net>
In-Reply-To: <4313AB8D.4010807@paradise.net.nz>
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> <43137AFB.9060304@mac.com> <20050829215613.GD1462@drjekyll.mkbuelow.net> <431390A0.5080007@mac.com> <20050830002051.GE1462@drjekyll.mkbuelow.net> <4313AB8D.4010807@paradise.net.nz>

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Mark Kirkwood wrote:

>Would you be happy if the handbook section added a caution, or referred 
>to the section that discusses the write cache?

Yes, that would inform the user.

>(FWIW - I have seen Linux + ext3 systems destroyed by power failure 
>because the admins refused to disable write caching on ATA drives - 
>Neither journelling or softupdates is much help if the HW is kidding you 
>about write acknowledgment).

>From what I understand from googling around on that issue, the
write-barrier stuff should make that much more unlikely. Of course
there could be the situation that it was a kernel that did not
(properly) support write-barriers yet, or the Linux implementation
has/had bugs (not too unlikely), or the disk was so broken that
even the flushing workaround strategies were ignored or it otherwise
didn't properly flush it, etc. But they're at least trying to cope
with the issue.  BTW., when have you last seen a broken NTFS? While
I don't do Windows much, I have had quite a few crashes on Windows
(2000, XP) over the years on various machines, and I always asked
myself how it could be that the system is up almost immediately
(probably due to log replay) with no discernible filesystem damage.
Windows (NT) has been doing the write barrier flush tricks (disabling-/
reenabling the cache for flushing it) for longer than Linux and I
would think that this contributes to the fault resilience of NTFS.
Not that I would imply that NTFS can't be corrupted, of course.

mkb.



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