# ZFS Metadata Eraser

`erase-zfs-metadata.sh` permanently overwrites disk metadata that can identify
a device as a ZFS vdev. It is intended for decommissioning or repurposing a
device after it has been cleanly removed from its pool.

## What It Erases

The script performs 10 overwrite passes with zeroes over the first 4 MiB and
the last 4 MiB of the target block device. These regions include:

- MBR data and GPT primary partition table at the beginning of a disk.
- GPT backup partition table at the end of a disk.
- The four conventional ZFS vdev-label regions, including their redundant
  copies at both ends of the device.

It does not overwrite the entire device. Data outside those metadata regions
may remain recoverable.

## Requirements

- Linux with Bash.
- Root privileges.
- `blockdev`, `dd`, `findmnt`, `lsblk`, and the ZFS `zpool` command.
- A target device of at least 8 MiB that is not mounted and is not part of an
  imported ZFS pool.

## Use

First, verify the target device carefully:

```bash
lsblk --output NAME,SIZE,TYPE,MOUNTPOINTS
zpool status -P
```

Then make the script executable and run it with the full block-device path:

```bash
chmod +x erase-zfs-metadata.sh
sudo ./erase-zfs-metadata.sh /dev/sdX
```

Replace `/dev/sdX` with the actual device, such as `/dev/sdb`,
`/dev/nvme0n1`, or a device-mapper path. Do not use the disk containing the
running system.

The script displays target details and requires this exact confirmation before
it writes anything:

```text
ERASE /dev/sdX
```

## Safety Behavior

Before overwriting, the script refuses to run when:

- The supplied path is not a block device.
- The device itself is mounted.
- A child partition of the device is mounted.
- `zpool status -P` shows the device in an imported pool.
- The device is smaller than 8 MiB.

These checks reduce common mistakes but are not a substitute for verifying the
device identity yourself. The operation is destructive and cannot be undone.

## Prepare a ZFS Device

For a device that belongs to a pool, first use the appropriate ZFS procedure,
such as replacing or detaching the vdev, then export the pool if necessary.
Confirm the target no longer appears in `zpool status -P` before running the
eraser. Do not use this utility to remove a live vdev from an active pool.

## Verify

After completion, inspect the device for residual filesystem or partition
signatures:

```bash
sudo wipefs --all --no-act /dev/sdX
sudo zdb -l /dev/sdX
```

`wipefs --no-act` reports signatures without modifying the device. `zdb -l`
should not find a readable ZFS label after a successful run.