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To: Alexander Best <arundel@freebsd.org>
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Date: Fri, 19 Aug 2011 10:52:17 -0700
From: Kirk McKusick <mckusick@mckusick.com>
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Cc: freebsd-fs@freebsd.org
Subject: Re: probably embarrassing SUJ question 
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> Date: Fri, 19 Aug 2011 17:40:33 +0000
> From: Alexander Best <arundel@freebsd.org>
> To: freebsd-fs@freebsd.org
> Subject: probably embarrassing SUJ question
> 
> Hi there,
> 
> I recently saw somebody using mount -o async in combination with
> gjournal. I just wanted to ask, whether async can also be used with
> SUJ? or will this put me in a dangerous situation, where my fs will
> get hosed after a crash?
> 
> cheers.
> alex

The async flag is incompatible with soft updates or journaled
soft updates. But not to fear, we added a seatbelt in ffs_mount:

	/*
	 * Soft updates is incompatible with "async",
	 * so if we are doing softupdates stop the user
	 * from setting the async flag in an update.
	 * Softdep_mount() clears it in an initial mount
	 * or ro->rw remount.
	 */
	if (MOUNTEDSOFTDEP(mp)) {
		MNT_ILOCK(mp);
		mp->mnt_flag &= ~MNT_ASYNC;
		MNT_IUNLOCK(mp);
	}

So, nothing bad will happen.

	Kirk McKusick