From: david@lang.hm Subject: Re: [patch] ext2/3: document conditions when reliable operation is possible Date: Tue, 25 Aug 2009 16:48:45 -0700 (PDT) Message-ID: References: <20090824212518.GF29763@elf.ucw.cz> <20090824223915.GI17684@mit.edu> <20090824230036.GK29763@elf.ucw.cz> <20090825000842.GM17684@mit.edu> <20090825094244.GC15563@elf.ucw.cz> <4A93E908.6050908@redhat.com> <20090825211515.GA3688@elf.ucw.cz> <4A9468E8.607@redhat.com> <20090825225114.GE4300@elf.ucw.cz> <4A946DD1.8090906@redhat.com> <20090825232601.GF4300@elf.ucw.cz> <4A947682.2010204@redhat.com> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Cc: Pavel Machek , Theodore Tso , Florian Weimer , Goswin von Brederlow , Rob Landley , kernel list , Andrew Morton , mtk.manpages@gmail.com, rdunlap@xenotime.net, linux-doc@vger.kernel.org, linux-ext4@vger.kernel.org, corbet@lwn.net To: Ric Wheeler Return-path: In-Reply-To: <4A947682.2010204@redhat.com> Sender: linux-doc-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Tue, 25 Aug 2009, Ric Wheeler wrote: > On 08/25/2009 07:26 PM, Pavel Machek wrote: >> >>>>> Basically, any file system (Linux, windows, OSX, etc) that writes into >>>>> the page cache will lose data when you hot unplug its storage. End of >>>>> story, don't do it! >>>> >>>> No, not ext3 on SATA disk with barriers on and proper use of >>>> fsync(). I actually tested that. >>>> >>>> Yes, I should be able to hotunplug SATA drives and expect the data >>>> that was fsync-ed to be there. >>> >>> You can and will lose data (even after fsync) with any type of storage at >>> some rate. What you are missing here is that data loss needs to be >>> measured in hard numbers - say percentage of installed boxes that have >>> config X that lose data. >> >> I'm talking "by design" here. >> >> I will lose data even on SATA drive that is properly powered on if I >> wait 5 years. >> > > You are dead wrong. > > For RAID5 arrays, you assume that you have a hard failure and a power outage > before you can rebuild the RAID (order of hours at full tilt). and that the power outage causes a corrupted write. >>> I can promise you that hot unplugging and replugging a S-ATA drive will >>> also lose you data if you are actively writing to it (ext2, 3, whatever). >> >> I can promise you that running S-ATA drive will also lose you data, >> even if you are not actively writing to it. Just wait 10 years; so >> what is your point? > > I lost a s-ata drive 24 hours after installing it in a new box. If I had MD5 > RAID5, I would not have lost any. me to, in fact just after I copied data from a raid array to it so that I could rebuild the raid array differently :-( David Lang