start   size  index  contents
      0      1         PMBR
      1      1         Pri GPT header
      2     32         Pri GPT table
     34   1024      1  GPT part - EFI System
   1058  19390      2  GPT part - NetBSD FFSv1/FFSv2
  20448     32         Sec GPT table
  20480      1         Sec GPT header