From mboxrd@z Thu Jan 1 00:00:00 1970 From: bugzilla-daemon@bugzilla.kernel.org Subject: [Bug 16490] "Assuming drive cache: write through" messages probably have wrong loglevel Date: Wed, 04 Jun 2014 14:19:03 +0000 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: Received: from mail.kernel.org ([198.145.19.201]:43929 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753236AbaFDOTM (ORCPT ); Wed, 4 Jun 2014 10:19:12 -0400 Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id E6DFD20328 for ; Wed, 4 Jun 2014 14:19:06 +0000 (UTC) Received: from bugzilla2.web.kernel.org (bugzilla2.web.kernel.org [172.20.200.52]) by mail.kernel.org (Postfix) with ESMTP id BD4EE202E5 for ; Wed, 4 Jun 2014 14:19:04 +0000 (UTC) In-Reply-To: Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: linux-scsi@vger.kernel.org https://bugzilla.kernel.org/show_bug.cgi?id=16490 Alain Kalker changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |a.c.kalker@gmail.com --- Comment #8 from Alain Kalker --- I submitted a patch to lower the log level to the linux-scsi mailing list. The patch was not accepted; James Bottomley offered this very insightful explanation why the log level should remain high (quoted here for those who are not reading the linux-scsi mailing list): > [...] The condition may be an error. We have > some USB attached storage devices with writeback caches which don't > supply caching information. Treating a writeback device as writethrough > is a potential error because you may lose data as a result of it. > > The error is that we've made an assumption which may damage your data. > > The problem for us is that we can't tell if the assumption is going to > be fatal or not ... the message is harmless for older USB devices. >>From doing a little research, I would suggest these steps to mitigate the risk (correct me if I'm wrong or have omitted anything): - Find out if the device has write cache enabled by default, by consulting its documentation, technical specifications, or by contacting the manufacturer. - If the device does have write cache enabled, a quirk parameter can be added to either the kernel commandline or as a module parameter for the usb-storage module[1] - Verify that the device works as expected. [1] For more information on USB storage device quirks and how to configure them, see linux/Documentation/kernel-parameters.txt in the Linux kernel source. -- You are receiving this mail because: You are the assignee for the bug.