Looking for that RAID ("smartd" and "mdadm")

It's nice to have a software raid in Linux in place, security is always good. But it's only as good as you let some daemon(s) check the status and let it report to you. Two highly recommended pieces of software are smartmontools (aka smartctl / smartd) and mdadm in daemon mode.
Assuming you're using Debian:
# apt-get install smartmontools
# apt-get install mdadm (probably already installed)

Depdending on what your /etc/mdadm/mdadm.conf says, better create a new config with mkconf:
# /usr/share/mdadm/mkconf
Don't forget to put your E-Mail address in it, like
MAILADDR you@domain.tld
Now, restart the daemon
# service mdadm restart
and send a testmail(!) to yourself using mdadm
# mdadm --monitor --scan --test --oneshot

Now for smartd, which will send you email about important S.M.A.R.T. values from your hdd(s).
# edit /etc/default/smartmontools
Enable this line:
and leave the others alone. Detailed settings follow here:
# edit /etc/smartd.conf
Comment out the one line that is enabled and put the following (to your hardware matching) line(s) in it:
/dev/sda -a -o off -S on -s (S/../.././02|L/../../6/03) -I 194 -m you@doman.tld
/dev/sdb -a -o off -S on -s (S/../.././02|L/../../6/03) -I 194 -m you@domain.tld
Hint: Depending on your distribution a DEVICESCAN-line is present, comment that one out.)

# service smartmontools restart
And with this service as well: Test(!) sending the mail:
# echo "/dev/sda -m you@domain.tld -M test" > /etc/smartd.conf.test
# smartd -c /etc/smartd.conf.test
Now for some final:
# service smartmontools restart
(Please recheck that smartd is now running without smartd.conf.test -> Otherwise "kill" and start the service normally)
And you're done!