From: Eric Sandeen Subject: Re: [PATCH] ext4: Ensure writecache to disk in no journal mode Date: Fri, 26 Mar 2010 12:40:04 -0500 Message-ID: <4BACF174.50703@redhat.com> References: <1269620462-25906-1-git-send-email-surbhi.palande@canonical.com> <87pr2rhwe0.fsf@openvz.org> <4BACEBE3.50108@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Dmitry Monakhov , Surbhi Palande , linux-ext4@vger.kernel.org, Theodore Tso To: Ric Wheeler Return-path: Received: from mx1.redhat.com ([209.132.183.28]:65066 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750772Ab0CZRkK (ORCPT ); Fri, 26 Mar 2010 13:40:10 -0400 In-Reply-To: <4BACEBE3.50108@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 03/26/2010 12:16 PM, Ric Wheeler wrote: > On 03/26/2010 12:37 PM, Dmitry Monakhov wrote: >> Surbhi Palande writes: >> >> >>> Ensure that in the no journal mode the write cache is flushed to the disk by >>> calling a blkdev_issue_flush() which issues a WRITE_BARRIER if necessary. >>> >> As soon as i understand, nojournal mode is assumed to be used for >> fail-free block devices(raid + UPS). So we don't have to worry about >> blkdev's wcache vs persistent storage correctness. No, I don't think so - even with "fail-free" storage, a system crash still results in an inconsistent filesystem; with nojournalling you've made the decision to either fsck or re-mkfs after that event. > I don't think that is a safe assumption. If users want that behavior, > they can mount with fs without barriers... yes, I agree with Ric - even if you don't have journalling, the proper sequence of sync calls should still result in data permanently on disk by default. (though I think using mount -o nobarrier for this purpose, in absence of journalling, overloads the option a little...) -Eric