Plesk 11.x / Linux :: How To Do MySQL Database Daily Backup Via Scheduled Tasks

I'm new to Parallels Panel. I use version 11.0.9. I want to backup mysql database daily. First of all, what is the best way for daily database backup in plesk. I'm trying to do this in Scheduled Tasks and I use mysqldump command although I'm not sure.

I chose the time and day first and then I switched on the task. I typed the following command to Command line.

mysqldump -uusername -ppassword databasename | gzip -9 >/httpdocs/mydatabase.sql.gz
or
mysqldump -uusername -ppassword databasename >/httpdocs/mydatabase.sql.gz

This created only a blank file. When I use this without gzip, nothing changes.

1- Is mysqldump right command for database backup?
2- Should I define full path for mysqldump, gzip and database? If so, how can I find out the full path of mysqldump, gzip and my database? Because I can't see their locations in panel.
3- I can't see any error message. There is not any log file in httpdocs folder. Where does the log file exist?
4- It is weird but should the username be "database user" or should I write "root" ?