RAID-Z Failure Notification
Solution 1:
Add this to /etc/periodic.conf:
daily_status_zfs_enable="YES"
Then you will have the status of your zfs pool added to the daily periodic emails that are sent. If you currently aren't receiving them you could add your email address in also via the variable:
daily_output="[email protected]"
Solution 2:
You could try something that queries and parses the output of zpool status via cron/email. Or a commercial solution at: http://www.santools.com/smartmonux.html
Solution 3:
chkdsk is one script you could run via cron that when properly configured will email you when zpool errors are detected.