From mboxrd@z Thu Jan 1 00:00:00 1970 From: Zheng Liu Subject: Re: Weird jbd2 I/O load Date: Tue, 22 Oct 2013 01:11:53 +0800 Message-ID: <52656059.4050000@gmail.com> References: <525DB679.4070008@redhost.ro> <20131021135338.GA3392@gmail.com> <5265392D.1020500@redhost.ro> <52655C78.4080507@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: linux-ext4@vger.kernel.org To: Andrei Banu Return-path: Received: from mail-pd0-f169.google.com ([209.85.192.169]:58149 "EHLO mail-pd0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751539Ab3JURL4 (ORCPT ); Mon, 21 Oct 2013 13:11:56 -0400 Received: by mail-pd0-f169.google.com with SMTP id q10so6549003pdj.28 for ; Mon, 21 Oct 2013 10:11:56 -0700 (PDT) In-Reply-To: <52655C78.4080507@gmail.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 10/22/2013 12:55 AM, Zheng Liu wrote: > On 10/21/2013 10:24 PM, Andrei Banu wrote: >> Hi Zheng, >> >> Thank you for your reply. We can make this test and if it doesn't help >> we'll re-enable >> the barrier but first I need to ask a few questions: >> >> 1. /dev/md2 is mounted on /. So your command should look like this? >> >> $ mount -t ext4 -o remount,barrier=0 /dev/md2 / > > Yes. > >> >> In /etc/fstab I have other parameters as well: >> noatime,usrjquota=quota.user,jqfmt=vfsv0 >> Do I also add these like this: >> >> $ mount -t ext4 -o >> remount,barrier=0,noatime,usrjquota=quota.user,jqfmt=vfsv0 /dev/md2 / > > If I remember correctly, this command is OK. But frankly I don't do the > test. I am not sure all these options will pass when you remount a > partition. > >> >> 2. Can the command above be run on an active (very active) cPanel server? > > Sorry, I am not familiar with cPanel server. But if your previous > testings run on a server under a heavy pressure. It quite impacts the > result because disk bandwidth is occupied by this process. Ah, sorry, I misunderstand your question. Yes, you can remount a partition on an active server. But as I said above, please do not run your testings on a server under heavy pressure because the result could be impacted. Regards, - Zheng > >> >> 3. How do I re-enable the barrier? > > sudo mount -t ext4 -o remount,barrier=1 ${DEV} ${MNT} > >> >> 4. What is the probability of data loss in case of cold reboot? > > After disabling barrier, the system couldn't ensure that the dirty data > has been written into the disk medium if your device couldn't support > FUA command. So I just want to make sure that your SSD can not handle > barrier command properly. *Please do not use 'barrier=0' in your > product system*. > > - Zheng > >> >> Thanks! >> >> On 10/21/2013 4:53 PM, Zheng Liu wrote: >>> Hi Andrei, >>> >>> Could you please disable barrier for ext4 and try your 'dd' test again? >>> $ sudo mount -t ext4 -o remount,barrier=0 ${DEV} ${MNT} >>> >>> *WARNING: you could lost your data with barrier=0 when you get a power >>> failure or cold reset.* >>> >>> We have met a similar problem that is because some SSDs couldn't handle >>> barrier command properly. >>> >>> Regards, >>> - Zheng >> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >