From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ric Wheeler Subject: Re: md: Change ENOTSUPP to EOPNOTSUPP Date: Tue, 02 May 2006 07:37:36 -0400 Message-ID: <44574480.8010405@emc.com> References: <20060428124313.29510.patches@notabene> <1060428025144.30770@suse.de> <62b0912f0604280634x7df2a8a5m9022826876446cb6@mail.gmail.com> <44524765.6070703@emc.com> <62b0912f0604290650v6fa0759flace16041c26fa003@mail.gmail.com> <4453CB4D.9020907@emc.com> <445633D4.2000607@fooplanet.com> <4456BBE4.2000706@steeleye.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4456BBE4.2000706@steeleye.com> Sender: linux-raid-owner@vger.kernel.org To: Paul Clements Cc: Gil , linux-raid@vger.kernel.org List-Id: linux-raid.ids Paul Clements wrote: > > You'll see something like this in your system log if barriers are not > supported: > > Apr 3 16:44:01 adam kernel: JBD: barrier-based sync failed on md0 - > disabling barriers > > > Otherwise, assume that they are. But like Neil said, it shouldn't > matter to a user whether they are supported or not. Filesystems will > work correctly either way. > > -- > Paul > File systems will work correctly, but if you are running without barriers and with your write cache enabled, you are running the risk of data loss or file system corruption on any power loss. It is an issue of concern since drive companies ship the write cache on by default. When we detect a non-supported drive (queuing enabled, lack of support for the barrier low level mechanism) we disable future barrier request and leave the write cache enabled. I guess that you could argue that this is what most home users want (i.e., best performance at the cost of some possible data loss on power outage since most people lose power rarely these days), but it is not good enough for critical data storage. I would suggest that if you see this message on ext3 (or the reiserfs message for reiser users), you should run with your write cache disabled by default or disable queuing (which is often the reason the barrier ops get disabled). ric