[CentOS] unable to umount

[Gordon Messmer]

On 02/25/2015 07:48 AM, Leon Fauster wrote:
> Am 22.02.2015 um 16:12 schrieb Stephen Harris <lists at spuddy.org>:
>> Is the device NFS exported?  I've seem that prevent umounting even though
>> nothing shows up in the process list.
>
> Its a local "virtual" device (raid controller exports it as one device).

I believe that Stephen was asking if you are exporting that filesystem 
via NFS to other systems.  Check /etc/exports.