I have a stack of SATA hard drives that I need to erase.

I have a USB drive dock, a box that a drive can be set into that connects to my computer via USB-3.

I am using DD to write zeros to the raw device, in this case, /dev/sdf.

No matter the actual size of the drive dd stops at about 3 to 7 gb. These are 300 gb to 3 TB drives.

I am not mounting the drives, but I do ensure they are visible to the system with lsblk. To change drives I turn off the dock. The drive then disappears from lsblk. When I insert a different drive and turn the dock back on again /dev/sdf re-appears.

Are all my drives bad? If they are I will need to have them “professionally” destroyed at about $25 a drive.