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Date: Fri, 27 Jul 2001 00:32:08 +1200
From: Chris Wedgwood <cw@f00f.org>
To: Andrew Morton <akpm@zip.com.au>
Cc: Matthias Andree <matthias.andree@stud.uni-dortmund.de>,
        lkml <linux-kernel@vger.kernel.org>,
        "ext3-users@redhat.com" <ext3-users@redhat.com>
Subject: Re: ext3-2.4-0.9.4
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On Thu, Jul 26, 2001 at 09:42:37PM +1000, Andrew Morton wrote:

    If postfix is capable of opening the files O_SYNC or of doing
    fsync() on them then the `chattr +s' is no longer necessary -
    unlike ext2, when the O_SYNC write() or the fsync() return, the
    directory contents (as well as the inode, bitmaps, data, etc) will
    all be tight on disk and will be restored after a crash.

    This should speed things up considerably, especially with
    journalled-data mode.  I need to test and characterise this some
    more to come up with some quantitative results and configuration
    recommendations.

Postfix does an fsync on file before closing them, it then does a
rename and expects once rename as returned, the renamed actually
occured --- even if the fs crashes.  It also expects if you fsync a
file, then it will appear in the parent directory with certainty and
not say /lost+found after fsck on reboot.

Without +s under ext2, you can loose file(s) in /lost+found because
open+write+fsync+close works and ensures the data is on disk, but the
parent directory doesn't get synced to disk, so it might get lost.




  --cw