I recently used a script to list all MySQL databases available in a Plesk server with the disk usage. You can find the script below.
Script to List Database Disk Usage in Plesk
if [ -d /var/lib/mysql ]; then echo -ne "nn=== MySQL DATABASES ===n"; mysql -uadmin -p`cat /etc/psa/.psa.shadow` -e "SELECT round(sum( data_length + index_length )/1024/1024,0) 'SM', table_schema 'DN' FROM information_schema.TABLES GROUP BY table_schema ORDER BY SM DESC G;" | sed '/***/d' | sed 's/SM: //' | sed ':a;N;$!ba;s/nDN:/Mt/g'; fi; === MySQL DATABASES === 128M wordpress_123 99M joomla_db 6M psa 1M mysql 1M sitebuilder3 1M apsc 0M phpmyadmin_o_4xzIaYJJqD 0M information_schema 0M phpmyadmin_0K_TUOFIGdTW 0M sitebuilder5 0M horde 0M atmail
Fell free to modify.
