From: Eric Sandeen Subject: Re: high write latency bug in ext3 / jbd in 3.4 Date: Mon, 13 Jan 2014 15:39:04 -0600 Message-ID: <52D45CF8.3030403@redhat.com> References: <20140113201320.GD1214@kvack.org> <99F82313-71DA-43E6-A071-05507183D481@dilger.ca> <20140113211610.GE1214@kvack.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Ext4 Developers List To: Benjamin LaHaise , Andreas Dilger Return-path: Received: from mx1.redhat.com ([209.132.183.28]:57536 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750962AbaAMVjM (ORCPT ); Mon, 13 Jan 2014 16:39:12 -0500 In-Reply-To: <20140113211610.GE1214@kvack.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 1/13/14, 3:16 PM, Benjamin LaHaise wrote: > On Mon, Jan 13, 2014 at 02:01:08PM -0700, Andreas Dilger wrote: >> Not to be flippant, but is there any reason NOT to just mount the >> filesystem with ext4? There are a large number of improvements in >> the ext4 code that don't require on-disk format changes (e.g. delayed >> allocation, multi-block allocation, etc) if there is a concern about >> being able to downgrade to an ext3-type mount in case of problems. > > I'm leaning towards doing this. The main reason for not doing so was > primarily that a few of the tweaks that I had been made to ext3 would > have to be ported to ext4. Thankfully, I think we're still in an early > enough stage of release that I should be able to do so. The changes > are pretty specific, mostly allocator tweaks to improve the on-disk > layout for our specific use-case. > >> There are further improvements in ext4 that can be used on upgraded >> ext3 filesystems if the feature bit is enabled (in particular extent >> mapped files). However, extent mapped files are not accessible under >> ext3, so it makes sense to run with ext4 w/o any new features for a >> while until you are sure it is working for you. > > I had hoped to use ext4, but the recommended fsck after changing the > various feature bits is a non-starter during our upgrade process (a 22 > minute outage isn't acceptable). I would never recommend the ext3-ext4 "tune2fs migration" - you'll end up with a really weird hybrid filesystems containing files with different capabilities, and missing many of the metadata layout improvements. -Eric