How to use all disk space on preinstalled Linux

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http://serverfault.com – I ordered dedicated server with Linux Debian Wheezy preinstalled with "Paralles Plesk Panel". Provider states I have 2x1TB drives. Yet my avaible disk space is just 100GB. Do I lack a partition? I don't know how to interpretate df -k the 79% usage where there's only 69 GB used as du -ch / shows. Do I have all space avaible to use? If not how to set it? $ sudo parted -l Model: ATA ST1000NM0011 (scsi) Disk /dev/sda: 1000GB Sector size (logical/physical): 512B/512B Partition Table: msdos Number Start End Size Type File system Flags 1 1049kB 100GB 100GB primary ext3 (HowTos)