Keep a second or third backup. If you want to be sure of the erased data you can simply drill few holes in them. But it’s a very extreme procedure. A two/three

Keep a second or third backup. If you want to be sure of the erased data you can simply drill few holes in them. But it’s a very extreme procedure. A two/three pass of “erase all data” is okay. HDD are not SSD that keeps the data when not “write 0 to safe erase the SSD”