From mboxrd@z Thu Jan 1 00:00:00 1970 From: Larkin Lowrey Subject: Re: Q wrt LVM snapshot of ext4 w/ external journal Date: Tue, 13 Apr 2010 16:06:41 -0500 Message-ID: <4BC4DCE1.3050600@nuclearwinter.com> References: <4BC4B66B.9000205@nuclearwinter.com> <20100413192257.GP1849@thunk.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: linux-ext4@vger.kernel.org To: tytso@mit.edu Return-path: Received: from titan.nuclearwinter.com ([209.40.204.131]:36256 "EHLO titan.nuclearwinter.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752246Ab0DMVGn (ORCPT ); Tue, 13 Apr 2010 17:06:43 -0400 In-Reply-To: <20100413192257.GP1849@thunk.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 4/13/2010 2:22 PM, tytso@mit.edu wrote: > It's safe to mount the LVM2 snapshot only if you use the mount option > noload. This will prevent it from using the journal, which is good, > since the journal is in use by the original file system. :-) > > I was able to verify that mounting with noload worked as advertised. Thank you. The exact message was "mounted filesystem without journal". > Hopefully, mounting the snapshot without using noload _should_ fail, > since the journal is already in use, but I'm not sure we have that > check in place, so I don't recommend trying it on a production file > system. I also verified that mounting w/o noload causes the mount operation to fail. The message was "failed to claim external journal device". When I unmounted the original fs so that the journal device was not in use and then tried to mount the snapshot w/o noload, the mounted snapshot was able to claim the journal. Of course I would never do that on purpose but I wanted to see what would happen. I believe this falls under the "don't do that or bad things will happen" category. Thank you very much for your response to my query. --Larkin