CentOS - Jan 2010 - /proc/mounts always shows "nobarrier" option for xfs, even when mounted with "barrier"

Ran into a confusing situation today.  When I mount an xfs filesystem on 
a server running centos 5.4 x86_64 with kernel 2.6.18-164.9.1.el5, the 
barrier/nobarrier mount option as displayed in /proc/mounts is always 
set to "nobarrier"

Here's an example:
[root at host ~]# mount -o nobarrier /dev/vg1/homexfs /mnt
[root at host ~]# grep xfs /proc/mounts
/dev/vg1/homexfs /mnt xfs rw,attr2,nobarrier,noquota 0 0
[root at host ~]# mount | grep xfs
/dev/mapper/vg1-homexfs on /mnt type xfs (rw,nobarrier)

[root at host ~]# mount -o barrier /dev/vg1/homexfs /mnt
[root at host ~]# grep xfs /proc/mounts
/dev/vg1/homexfs /mnt xfs rw,attr2,nobarrier,noquota 0 0
[root at host ~]# mount | grep xfs
/dev/mapper/vg1-homexfs on /mnt type xfs (rw,barrier)

Can anyone else confirm this behavior?

Thanks,
Tom

On Jan 21, 2010, at 4:04 PM, Tom Georgoulias <tomg at
mcclatchyinteractive.com
 > wrote:
> Ran into a confusing situation today.  When I mount an xfs  
> filesystem on
> a server running centos 5.4 x86_64 with kernel 2.6.18-164.9.1.el5, the
> barrier/nobarrier mount option as displayed in /proc/mounts is always
> set to "nobarrier"
>
> Here's an example:
> [root at host ~]# mount -o nobarrier /dev/vg1/homexfs /mnt
> [root at host ~]# grep xfs /proc/mounts
> /dev/vg1/homexfs /mnt xfs rw,attr2,nobarrier,noquota 0 0
> [root at host ~]# mount | grep xfs
> /dev/mapper/vg1-homexfs on /mnt type xfs (rw,nobarrier)
>
> [root at host ~]# mount -o barrier /dev/vg1/homexfs /mnt
> [root at host ~]# grep xfs /proc/mounts
> /dev/vg1/homexfs /mnt xfs rw,attr2,nobarrier,noquota 0 0
> [root at host ~]# mount | grep xfs
> /dev/mapper/vg1-homexfs on /mnt type xfs (rw,barrier)
>
> Can anyone else confirm this behavior?
LVM doesn't support barriers.

-Ross