From: Theodore Ts'o Subject: Re: ext4 filesystem bad extent error review Date: Fri, 3 Jan 2014 13:06:54 -0500 Message-ID: <20140103180654.GC4336@thunk.org> References: <20140102184211.GC10870@thunk.org> <20140103154846.GB31411@thunk.org> <52C6F22A.4040202@redhat.com> <20140103175111.GA4336@thunk.org> <52C6F944.4030605@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Huang Weller (CM/ESW12-CN)" , "linux-ext4@vger.kernel.org" , "Juergens Dirk (CM-AI/ECO2)" To: Eric Sandeen Return-path: Received: from imap.thunk.org ([74.207.234.97]:45687 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751039AbaACSHB (ORCPT ); Fri, 3 Jan 2014 13:07:01 -0500 Content-Disposition: inline In-Reply-To: <52C6F944.4030605@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Fri, Jan 03, 2014 at 11:54:12AM -0600, Eric Sandeen wrote: > > > > This call chain only happens if the block device is mounted. > > Sure, but I thought that's what they were doing. Maybe I misread. > I thought this was in relation to doing what they called a "barrier test", where you are writing to flash device and then drop power, and then see if the CACHE FLUSH request was actually honored. (And whether or not the FTL got corrupted so badly that the device brick's itself, as does happen for some of the crappier cheap flash out there.) But I'm not sure precisely how they implemented their test. It's possible it was done with the file system mounted. My suggestion was to make sure that the flash was proof against power drops by doing this using a raw block device, to remove the variable of the file system. Given that they've since reported that they can repro the problem using soft resets, it doesn't sound like the problem is related to flash devices not handling powe drops correctly --- although given that I'm still getting reports of people who have had their SD card get completely bricked after a power drop event, it's unfortunately not a solved problem by the flash manufacturers yet.... or rather, the few (many?) bad apples give all low-end flash a bad name. - Ted