From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: with ECARTIS (v1.0.0; list xfs); Thu, 20 Dec 2007 17:55:29 -0800 (PST) Received: from cuda.sgi.com (cuda1.sgi.com [192.48.168.28]) by oss.sgi.com (8.12.11.20060308/8.12.11/SuSE Linux 0.7) with ESMTP id lBL1tMdT027100 for ; Thu, 20 Dec 2007 17:55:25 -0800 Received: from email.msoe.edu (localhost [127.0.0.1]) by cuda.sgi.com (Spam Firewall) with ESMTP id B911AB8F2AC for ; Thu, 20 Dec 2007 17:55:35 -0800 (PST) Received: from email.msoe.edu (email.msoe.edu [155.92.194.61]) by cuda.sgi.com with ESMTP id n83GoDDegsoLHZFv for ; Thu, 20 Dec 2007 17:55:35 -0800 (PST) Date: Thu, 20 Dec 2007 19:55:33 -0600 From: "Jonathan C. Detert" Subject: Re: mount prob: "log inconsistent or not a log" Message-ID: <20071221015533.GH6476@msoe.edu> References: <20071220000144.GQ19770@msoe.edu> <4769BD13.5040303@sgi.com> <20071220011848.GV19770@msoe.edu> <20071220015425.GL4612@sgi.com> <20071220024453.GX19770@msoe.edu> <20071220175512.GA6023@msoe.edu> <476B0D29.4050504@sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <476B0D29.4050504@sgi.com> Sender: xfs-bounce@oss.sgi.com Errors-to: xfs-bounce@oss.sgi.com List-Id: xfs To: xfs@oss.sgi.com * Timothy Shimmin [071220 18:49]: > Jonathan C. Detert wrote: > > > >I just want to clarify - I mean to ask: > > > > Is it possible that an xfs filesystem which is in use by an o.s., > > last mounted by the o.s. months ago, could have a corrupted log, and > > yet keep functioning until such time as a remount of it is attempted? > > > Yes. > The log is read on every mount. I don't believe we read it otherwise. > On a mount we look for the log head and an unmount record etc. to decide > whether to do a replay or not. > So it could be corrupted and we would not know and we don't really care > until the next mount. > However, if we are modifying metadata in the filesystem (with some > exceptions) > then we will be continuing to write to the log and we will continue to > wrap the log. And hence if someone corrupted the log at a point in the past, > we may very well be able to overwrite the log and effectively lose that > corruption. > > Do you understand the basic idea? I think so. > We just write to the log while the file-system is mounted and we are writing > to the filesystem (particularly changing metadata); and > we read from the log during (just prior) mounting of the filesystem. > > > I.e. if a log gets corrupted while the f.s. is in use, will anyone > > notice, until such time as an attempt to remount the f.s. is made? > No I don't think anyone will notice. > No-one has cause to read it, so noone cares. > > If you unmount it cleanly. Run repair on it before mounting it again. > Then repair may find corruption when it tries to find the log head etc... > to work out if the log is clean or not. > i.e. in this case repair will try to read the log before you've tried > to do a mount. So, how do you recover from a situation like i have, namely: 1) the xfs file system is not currently mounted 2) an attempt to mount the xfs fs fails, complaining about log being inconsistent or not a log You say noone cares if the log is corrupt, but it seems to be a fatal problem if you want to mount the fs. Bottom line: how do you recover when trying to remount an xfs fs whose log happens to be corrupt? -- Jon Detert IT Systems Administrator, Milwaukee School of Engineering 1025 N. Broadway, Milwaukee, Wisconsin 53202, U.S.A. -- "Solitary trees, if they grow at all, grow strong." ~ Winston Churchill