linux-ext4 - Re: Weird jbd2 I/O load

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Date:	Mon, 21 Oct 2013 17:24:45 +0300
From:	Andrei Banu <andrei.banu@...host.ro>
To:	linux-ext4@...r.kernel.org
Subject: Re: Weird jbd2 I/O load

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    /

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     /

2. Can the command above be run on an active (very active) cPanel server?

3. How do I re-enable the barrier?

4. What is the probability of data loss in case of cold reboot?

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

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