# Guide: Repurpose Old Windows BitLocker Drive as /home on Arch Linux

## Environment
- OS: CachyOS (Arch-based) with btrfs root
- Existing /home: btrfs subvolume (@home) on OS drive
- Secondary drive: 954GB NVMe with Windows BitLocker partition

## Goal

Wipe the old Windows drive and mount it as `/home` on ext4, giving a dedicated large partition for user data separate from the OS.

## Steps

### Step 1: Identify the Drive

```bash
lsblk -o NAME,SIZE,TYPE,FSTYPE,MOUNTPOINT,MODEL
```

Output:
```
nvme0n1     953.9G disk                      SKHynix_HFS001TEJ9X115N
├─nvme0n1p1     4G part vfat      /boot
└─nvme0n1p2 949.9G part btrfs     /root       <-- OS drive
nvme1n1     953.9G disk                      SKHynix_HFS001TEJ9X115N
├─nvme1n1p1    16M part                       <-- Windows MSR
└─nvme1n1p2 953.9G part BitLocker             <-- Target drive
```

### Step 2: Wipe and Partition

```bash
# Wipe all filesystem signatures
sudo wipefs -a /dev/nvme1n1

# Create GPT table with single ext4 partition
sudo parted /dev/nvme1n1 --script mklabel gpt mkpart primary ext4 0% 100%

# Format with label
sudo mkfs.ext4 -L home /dev/nvme1n1p1
```

### Step 3: Copy Existing /home

```bash
# Mount new partition temporarily
sudo mount /dev/nvme1n1p1 /mnt

# Copy everything preserving permissions, ACLs, and extended attributes
sudo rsync -aAXv /home/ /mnt/

# Verify
ls -la /mnt/yourusername/
du -sh /mnt/yourusername/

# Unmount
sudo umount /mnt
```

### Step 4: Get UUID

```bash
sudo blkid /dev/nvme1n1p1
# UUID="4143f922-455f-4154-8f87-6df123548916" TYPE="ext4"
```

### Step 5: Update /etc/fstab

Replace the existing `/home` mount entry. If coming from a btrfs subvolume setup:

```bash
# BEFORE (btrfs subvolume):
# UUID=8a8b1d34-... /home btrfs subvol=/@home,defaults,noatime,compress=zstd:1 0 0

# AFTER (ext4 on new drive):
UUID=4143f922-455f-4154-8f87-6df123548916 /home ext4 defaults,noatime 0 2
```

### Step 6: Reboot

```bash
sudo reboot
```

### Step 7: Verify After Reboot

```bash
df -h /home
# Should show /dev/nvme1n1p1 mounted at /home with ~938GB available

mount | grep home
# /dev/nvme1n1p1 on /home type ext4 (rw,noatime)
```

## Notes

- The old btrfs `@home` subvolume remains on the OS drive as an automatic backup. You can delete it later with `sudo btrfs subvolume delete /path/to/@home` if you need the space.
- ext4 was chosen over btrfs for the /home drive for simplicity and maximum compatibility. If you prefer btrfs features (snapshots, compression), use `mkfs.btrfs` instead.
- The `noatime` mount option reduces unnecessary writes by not updating file access timestamps.
- Pass `0 2` in fstab (not `0 0`) so fsck runs on boot if needed, but after the root filesystem (which is `0 1`).
