Since my servers often run for weeks (or months) without me seeing them. It's nice to be notified if something goes wrong.
First you need to install smartmon tools
apt-get install smartmontools
Then edit smartd.conf
And add this line
DEVICESCAN -l error -l selftest -s (S/../.././01) -m email@example.com
This will run a short self test every night at 1:00am and email you if there are any errors. This has notified me of two disk failures so far.