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To: Alfred Perlstein <bright@wintelcom.net>
Subject: Re: changing mount options still can cause damage? 
Cc: fs@freebsd.org
In-reply-to: Your message of "Sun, 20 Feb 2000 03:19:38 PST."
             <20000220031938.D21720@fw.wintelcom.net> 
Date: Mon, 21 Feb 2000 16:00:51 -0800
From: Kirk McKusick <mckusick@flamingo.McKusick.COM>
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	Date: Sun, 20 Feb 2000 03:19:38 -0800
	From: Alfred Perlstein <bright@wintelcom.net>
	To: fs@freebsd.org
	Cc: mckusick@freebsd.org
	Subject: changing mount options still can cause damage?

	Is it true that we can still cause major damage to filesystems that
	are moved from read-only to read-write or noasync <-> async?

	>From the mount manpage:

	--
	BUGS
	 It is possible for a corrupted file system to cause a crash.

	 Switching a filesystem back and forth between asynchronous and
	 normal operation or between read/write and read/only access
	 using ``mount -u'' may gradually bring about severe filesystem
	 corruption.
	--

	The first bug is understandable, but personally I've never seen the
	second happen, is this still a real problem?

	If not I'd like to remove it.

	thanks,
	-- 
	-Alfred Perlstein - [bright@wintelcom.net|alfred@freebsd.org]

Switching between read-only and read-write should never cause filesystem
corruption. Running async can certainly lead to corruption if the
system crashes. There is an indeterminate period of time after the
system has been switched from async to sync before it will be stable
again, but that period will rarely be more than a minute or two. The
act of switching between sync and async should not cause corruption.
It is just the inherent risk of corruption while running async.

	Kirk McKusick


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