How can I quickly wipe a disk (filesystem/partitions) without overwriting all content with random data? For example
shred could accomplish what I want but takes to much time.
If you don't care about actually destroying the data on the disk, you can probably do something like
dd if=/dev/urandom of=/dev/sdc bs=1M count=2 to fry the first couple of megabytes (which would include the MBR and partition table).
Be super-duper sure about which block device you point at as there are no taksey-backsies on this command
ATA Secure Erase is available on non-SSD drives, too. See https://askubuntu.com/questions/42266/what-is-the-recommended-way-to-empty-a-ssd on how to request the operation.