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btrfs-layout.md

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Btrfs Subvolume Layout

Recommended Structure

Volume (/)
├── @           → /           (OS, snapshotted)
├── @home       → /home       (user data, snapshotted separately)
├── @nix        → /nix        (reproducible, exclude or infrequent)
├── @snapshots  → /.snapshots (Snapper metadata)
└── @var_log    → /var/log    (exclude from snapshots)

Why?

  • @: OS files, snapshotted before every zypper update
  • @home: User data, daily snapshots, kept longer
  • @nix: Reproducible from flake.lock, can exclude or snapshot less often
  • @snapshots: Required for Snapper metadata
  • @var_log: Log files, no snapshots (waste space)

Setup (during install or first boot)

If you're using the KIWI ISO, you'll need to create these manually on first boot OR extend the KIWI config to create them.

Manual Setup (post-install)

# Identify root device
ROOTDEV=$(findmnt -no SOURCE /)

# Mount top-level subvolume
sudo mkdir -p /mnt/btrfs
sudo mount "$ROOTDEV" /mnt/btrfs -o subvolid=5

# Create subvolumes
cd /mnt/btrfs
sudo btrfs subvolume create @nix
sudo btrfs subvolume create @var_log

# Update /etc/fstab
UUID=$(blkid -s UUID -o value "$ROOTDEV")
cat <<EOF | sudo tee -a /etc/fstab
UUID=$UUID /nix      btrfs subvol=@nix,compress=zstd,noatime 0 0
UUID=$UUID /var/log  btrfs subvol=@var_log,compress=zstd,noatime 0 0
EOF

# Mount
sudo mkdir -p /nix /var/log
sudo mount /nix
sudo mount /var/log

# Migrate existing data
sudo rsync -a /var/log.old/ /var/log/ && sudo rm -rf /var/log.old

sudo umount /mnt/btrfs

Snapper Configuration

Root subvolume (@)

  • Timeline: hourly (keep 10), daily (keep 7), weekly (keep 4)
  • Number cleanup: keep last 10
  • Triggered by zypper (pre/post snapshots)

Home subvolume (@home)

sudo snapper -c home create-config /home
sudo snapper -c home set-config TIMELINE_CREATE=yes
sudo snapper -c home set-config TIMELINE_LIMIT_HOURLY=0
sudo snapper -c home set-config TIMELINE_LIMIT_DAILY=7
sudo snapper -c home set-config TIMELINE_LIMIT_WEEKLY=4
sudo snapper -c home set-config TIMELINE_LIMIT_MONTHLY=6

Nix subvolume (@nix)

# Option 1: No snapshots (fully reproducible)
sudo snapper -c nix create-config /nix
sudo snapper -c nix set-config TIMELINE_CREATE=no

# Option 2: Weekly snapshots (if you want faster recovery)
sudo snapper -c nix set-config TIMELINE_CREATE=yes
sudo snapper -c nix set-config TIMELINE_LIMIT_HOURLY=0
sudo snapper -c nix set-config TIMELINE_LIMIT_DAILY=0
sudo snapper -c nix set-config TIMELINE_LIMIT_WEEKLY=2

Verification

# List subvolumes
sudo btrfs subvolume list /

# Check mount points
findmnt -t btrfs

# Snapper configs
sudo snapper list-configs

# Storage usage
sudo btrfs filesystem usage /