KDiskMark is an HDD and SSD benchmark tool with a very friendly graphical user interface.
GParted Partition Editor
GParted is a free partition editor for graphically managing your disk partitions.
GNOME Disks
GNOME Disks, gnome-disk-image-mounter und gsd-disk-utility-notify sind Bibliotheken und Anwendungen für den Umgang mit Speichermedien.
Disk Usage Analyzer
Disk Usage Analyzer is a graphical application to analyse disk usage in any Gnome environment.