FYI, unless you have a freshly installed SL6.1 machine, it is likely
that you will not receive email from mdadm when your array fails. This
is because mdadm is not runing. It looks like it always crashes
on startup unless all md arrays have metadata version 1.0 or later -
there is a version number listed in /proc/mdstat - if there is an array
without version number, mdstat will crash. This was found and fixed
in Fedora.

For more details, see
https://bugzilla.redhat.com/show_bug.cgi?id=787276

P.S. Aparently this problem is fixed in RHEL/SL6.2:

cd /triumfcs/mirror/SL/6.2/x86_64/os/Packages
rpm -vh --upgrade mdadm-3.2.2-9.el6.x86_64.rpm
service mdmonitor restart
no mdadm crash
got many emails from mdadm
mdadm still running.

-- 
Konstantin Olchanski
Data Acquisition Systems: The Bytes Must Flow!
Email: olchansk-at-triumf-dot-ca
Snail mail: 4004 Wesbrook Mall, TRIUMF, Vancouver, B.C., V6T 2A3, Canada