From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andreas Dilger Subject: Re: Ext4 MAX journal size ? Date: Mon, 07 Dec 2009 15:16:07 -0700 Message-ID: <3470552D-0538-4F6E-BEA4-E85C97148E87@sun.com> References: <4B1D77B1.8090805@icdsoft.com> Mime-Version: 1.0 Content-Type: text/plain; CHARSET=US-ASCII; delsp=yes; format=flowed Content-Transfer-Encoding: 7BIT Cc: linux-ext4@vger.kernel.org To: Iavor Stoev Return-path: Received: from sca-es-mail-2.Sun.COM ([192.18.43.133]:62903 "EHLO sca-es-mail-2.sun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933464AbZLGWQH (ORCPT ); Mon, 7 Dec 2009 17:16:07 -0500 Received: from fe-sfbay-10.sun.com ([192.18.43.129]) by sca-es-mail-2.sun.com (8.13.7+Sun/8.12.9) with ESMTP id nB7MGDqP014443 for ; Mon, 7 Dec 2009 14:16:14 -0800 (PST) Received: from conversion-daemon.fe-sfbay-10.sun.com by fe-sfbay-10.sun.com (Sun Java(tm) System Messaging Server 7u2-7.04 64bit (built Jul 2 2009)) id <0KUA00G00YYJLH00@fe-sfbay-10.sun.com> for linux-ext4@vger.kernel.org; Mon, 07 Dec 2009 14:16:13 -0800 (PST) In-reply-to: <4B1D77B1.8090805@icdsoft.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 2009-12-07, at 14:46, Iavor Stoev wrote: > I wonder if the Ext3's MAX journal size of 102,400 file system blocks > has been increased in Ext4. > > I'm using 10TB 4k block Ext3 file system with external journal on > Gigabyte I-Ram drive and I'm planning a migration to Ext4 system. > And I wonder if I can increase the journal size over 400MB. Well, even with ext3 the maximum journal size was only for internal journals. It was always possible to have larger external journal devices. With ext4, the maximum journal size WAS increased, though this is in fact a mke2fs/tune2fs limit so it is also increased for new ext3 filesystems. Note that with large journals you are also consuming an equal amount of RAM as the size of the journal, so don't make it crazy big. Having a journal on SSD is only really noticable for sync-happy workloads. It isn't noticably better than using a regular disk for the external journal if you aren't doing a lot of syncs (e.g. NFS or email). I've thought in the past that it might be an interesting hack to use a huge journal device (say 32GB) with data journaling, and then have the JBD layer get the data blocks from the journal for checkpointing to the filesystem instead of keeping the buffers pinned in RAM. That would would allow blazing metadata workloads, zero seeking, and then checkpointing in bulk to the filesystem. ... but unfortunately not something I have time to test out. Cheers, Andreas -- Andreas Dilger Sr. Staff Engineer, Lustre Group Sun Microsystems of Canada, Inc.