wipe.sh

#!/bin/bash
## Some commands and/or syntax are targeted for FreeBSD and more
## precisely NAS4Free 9.2.*.* series.
## The script will probably fail if used in Linux or more limited
## FreeBSD environments.
## You have been warned.
##
## The purpose of the script is to zero out the first and last 4Mb
## of the disk targeted for disks reporting 512byte sector-size.
## For disks that actually report a 4k sector size, it will wipe
## out the first and last 32Mb.
## Many disks still false-report a 512byte sector when they are in
## fact 4k drives, due to backwards (and isn't it always)
## compatibility with windows.
## The purpose is to wipe out the MBR and GPT partition tables and
## ZFS fingerprints that may exist on a drive.
## Ever have a drive with a single ZFS pool, but "zpool import"
## shows three or more possible pools to try to import from the
## drive (due to reuse/testing)?  I have.
## After using this, the drive will appear to be blank.  It isn't.
## But plugging the drive into windows, Linux, FreeBSD, or Android,
## it will appear to be, and can be partitioned and formatted for
## use as you see fit.  Of course forensic scans of the disk would
## still return data from the previous usage, but for home users
## this simplifies readying the disk for use in a different
## capacity than previous.
##
echo "What disk do you want"
echo "to wipe? For example - ada1 :"
read disk
echo "OK, in 10 seconds I will destroy all data on $disk!"
echo "Press CTRL+C to abort!"
sleep 10
diskinfo ${disk} | while read disk sectorsize size sectors other
do
    echo Deleting MBR, GPT Primary, ZFS(L0L1)/other partition tables.
    /bin/dd if=/dev/zero of=/dev/${disk} bs=${sectorsize} count=8196
    echo Deleting GEOM metadata, GPT Secondary(L2L3).
    /bin/dd if=/dev/zero of=/dev/${disk} bs=${sectorsize} oseek=$(expr $sectors - 8196) count=8196
done