From: Andreas Dilger Subject: Re: [RFC][PATCH] Multiple mount protection Date: Fri, 1 Jun 2007 03:14:35 -0600 Message-ID: <20070601091435.GR5181@schatzie.adilger.int> References: <1179777153.3910.13.camel@garfield> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Kalpak Shah , linux-ext4 To: Andi Kleen Return-path: Received: from mail.clusterfs.com ([206.168.112.78]:33091 "EHLO mail.clusterfs.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755411AbXFAJOh (ORCPT ); Fri, 1 Jun 2007 05:14:37 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-ext4-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Jun 01, 2007 10:46 +0200, Andi Kleen wrote: > Kalpak Shah writes: > > There have been reported instances of a filesystem having been > mounted at 2 places at the same time causing a lot of damage to the > filesystem.... The superblock will have a block number (s_mmp_block) > which will hold a MMP structure which has a sequence number which will be > periodically updated every 5 seconds by a mounted filesystem. > > That will make laptop users very unhappy if you spin up their disks every > 5 seconds. And even on other systems it might reduce the MTBF if you > write the super block much more often than before. It might be better to > set it up in some way to only increase that number when the super block is > written for some other reason anyways. It was mentioned before but deserves mentioning again that this will be an optional feature, mostly for use on SANs, iSCSI, etc where a disk might be accessed by multiple nodes at the same time. That means there will not be any impact for desktop users waiting 10s for each of their filesystems to mount. Cheers, Andreas -- Andreas Dilger Principal Software Engineer Cluster File Systems, Inc.