Resolution
We cannot give any exact numbers, however, you should take into account the following.Plesk for Linux OSes stores all users' data in /var partition by default, so the partitioning should be like:
SWAP -> twice RAM size
/boot -> 128 MB
/ -> System + Plesk, updates. 5-10 GB should be enough.
/tmp -> 1GB.
/var -> the rest of the space (domains, mail, backups, databases are stored there)
Directories that usually take much disk space:
/var/www/vhosts (/srv/vhosts on SuSE) - domains.
/var/qmail - mail.
/var/lib/mysql - Mysql databases.
/var/lib/psa/dumps - Plesk clients'/domains' backups.
/var/lib/pgsql/data - Postgres databases.
/var/tomcat* - Tomcat applications.
/var/lib/mailman - Mailman lists.
Please check file /etc/psa/psa.conf for all other directories used by Plesk control panel.
Plesk Contorl Panel under FreeBSD uses the /usr/local partition for storing large quantity of data and /var/db partition for databases.
So the /usr and /var partitions have to be larger in this case.
On Debian and Ubuntu, Plesk itself is located in /opt/psa.
Currently supported operating systems can be found on the product requirements page at http://www.parallels.com/en/products/plesk/reqs.
Keywords: partitions; directories; disc size