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+TODO:
+
+r0, r1, r2: add ``
+
+# f3s: Kubernetes with FreeBSD - Part 6: Storage
+
+This is the sixth blog post about the f3s series for self-hosting demands in a home lab. f3s? The "f" stands for FreeBSD, and the "3s" stands for k3s, the Kubernetes distribution used on FreeBSD-based physical machines.
+
+<< template::inline::index f3s-kubernetes-with-freebsd-part
+
+=> ./f3s-kubernetes-with-freebsd-part-1/f3slogo.png f3s logo
+
+<< template::inline::toc
+
+## Introduction
+
+In the previous posts, we set up a FreeBSD-based Kubernetes cluster using k3s. While the base system works well, Kubernetes workloads often require persistent storage for databases, configuration files, and application data. Local storage on each node has significant limitations:
+
+* No data sharing: Pods (once we run Kubernetes) on different nodes can't access the same data
+* Pod mobility: If a pod moves to another node, it loses access to its data
+* No redundancy: Hardware failure means data loss
+
+This post implements a robust storage solution using:
+
+* CARP: For high availability with automatic IP failover
+* NFS over stunnel: For secure, encrypted network storage
+* ZFS: For data integrity, encryption, and efficient snapshots
+* `zrepl`: For continuous ZFS replication between nodes
+
+The result is a highly available, encrypted storage system that survives node failures while providing shared storage to all Kubernetes pods.
+
+Other than what was mentioned in the first post of this blog series, we aren't using HAST, but `zrepl` for data replication. Read more about it later in this blog post.
+
+## Additional storage capacity
+
+We add 1 TB of additional storage to each of the nodes (`f0`, `f1`, `f2`) in the form of an SSD drive. The Beelink mini PCs have enough space in the chassis for the extra space.
+
+=> ./f3s-kubernetes-with-freebsd-part-6/drives.jpg
+
+Upgrading the storage was as easy as unscrewing, plugging the drive in, and then screwing it back together again. The procedure was uneventful! We're using two different SSD models (Samsung 870 EVO and Crucial BX500) to avoid simultaneous failures from the same manufacturing batch.
+
+We then create the `zdata` ZFS pool on all three nodes:
+
+```sh
+paul@f0:~ % doas zpool create -m /data zdata /dev/ada1
+paul@f0:~ % zpool list
+NAME    SIZE  ALLOC   FREE  CKPOINT  EXPANDSZ   FRAG    CAP  DEDUP    HEALTH  ALTROOT
+zdata   928G  12.1M   928G        -         -     0%     0%  1.00x    ONLINE  -
+zroot   472G  29.0G   443G        -         -     0%     6%  1.00x    ONLINE  -
+
+paul@f0:/ % doas camcontrol devlist
+<512GB SSD D910R170>               at scbus0 target 0 lun 0 (pass0,ada0)
+<Samsung SSD 870 EVO 1TB SVT03B6Q>  at scbus1 target 0 lun 0 (pass1,ada1)
+paul@f0:/ %
+```
+
+To verify that we have a different SSD on the second node (the third node has the same drive as the first):
+
+```sh
+paul@f1:/ % doas camcontrol devlist
+<512GB SSD D910R170>               at scbus0 target 0 lun 0 (pass0,ada0)
+<CT1000BX500SSD1 M6CR072>          at scbus1 target 0 lun 0 (pass1,ada1)
+```
+
+## ZFS encryption keys
+
+ZFS native encryption requires encryption keys to unlock datasets. We need a secure method to store these keys that balances security with operational needs:
+
+* Security: Keys must not be stored on the same disks they encrypt
+* Availability: Keys must be available at boot for automatic mounting
+* Portability: Keys should be easily moved between systems for recovery
+
+Using USB flash drives as hardware key storage provides a convenient and elegant solution. The encrypted data is unreadable without physical access to the USB key, protecting against disk theft or improper disposal. In production environments, you may use enterprise key management systems; however, for a home lab, USB keys offer good security with minimal complexity.
+
+### UFS on USB keys
+
+We'll format the USB drives with UFS (Unix File System) rather than ZFS for simplicity. There is no need to use ZFS.
+
+Let's see the USB keys:
+
+=> ./f3s-kubernetes-with-freebsd-part-6/usbkeys1.jpg USB keys
+
+To verify that the USB key (flash disk) is there:
+
+```
+paul@f0:/ % doas camcontrol devlist
+<512GB SSD D910R170>               at scbus0 target 0 lun 0 (pass0,ada0)
+<Samsung SSD 870 EVO 1TB SVT03B6Q>  at scbus1 target 0 lun 0 (pass1,ada1)
+<Generic Flash Disk 8.07>          at scbus2 target 0 lun 0 (da0,pass2)
+paul@f0:/ %
+```
+
+Let's create the UFS file system and mount it (done on all three nodes `f0`, `f1` and `f2`):
+
+```sh
+paul@f0:/ % doas newfs /dev/da0
+/dev/da0: 15000.0MB (30720000 sectors) block size 32768, fragment size 4096
+        using 24 cylinder groups of 625.22MB, 20007 blks, 80128 inodes.
+        with soft updates
+super-block backups (for fsck_ffs -b #) at:
+ 192, 1280640, 2561088, 3841536, 5121984, 6402432, 7682880, 8963328, 10243776,
+11524224, 12804672, 14085120, 15365568, 16646016, 17926464, 19206912,k 20487360,
+...
+
+paul@f0:/ % echo '/dev/da0 /keys ufs rw 0 2' | doas tee -a /etc/fstab
+/dev/da0 /keys ufs rw 0 2
+paul@f0:/ % doas mkdir /keys
+paul@f0:/ % doas mount /keys
+paul@f0:/ % df | grep keys
+/dev/da0             14877596       8  13687384     0%    /keys
+```
+
+=> ./f3s-kubernetes-with-freebsd-part-6/usbkeys2.jpg USB keys stuck in
+
+### Generating encryption keys
+
+The following keys will later be used to encrypt the ZFS file systems. They will be stored on all three nodes, serving as a backup in case one of the keys is lost or corrupted. When we later replicate encrypted ZFS volumes from one node to another, the keys must also be available on the destination node.
+
+```
+paul@f0:/keys % doas openssl rand -out /keys/f0.lan.buetow.org:bhyve.key 32
+paul@f0:/keys % doas openssl rand -out /keys/f1.lan.buetow.org:bhyve.key 32
+paul@f0:/keys % doas openssl rand -out /keys/f2.lan.buetow.org:bhyve.key 32
+paul@f0:/keys % doas openssl rand -out /keys/f0.lan.buetow.org:zdata.key 32
+paul@f0:/keys % doas openssl rand -out /keys/f1.lan.buetow.org:zdata.key 32
+paul@f0:/keys % doas openssl rand -out /keys/f2.lan.buetow.org:zdata.key 32
+paul@f0:/keys % doas chown root *
+paul@f0:/keys % doas chmod 400 *
+
+paul@f0:/keys % ls -l
+total 20
+*r--------  1 root wheel 32 May 25 13:07 f0.lan.buetow.org:bhyve.key
+*r--------  1 root wheel 32 May 25 13:07 f1.lan.buetow.org:bhyve.key
+*r--------  1 root wheel 32 May 25 13:07 f2.lan.buetow.org:bhyve.key
+*r--------  1 root wheel 32 May 25 13:07 f0.lan.buetow.org:zdata.key
+*r--------  1 root wheel 32 May 25 13:07 f1.lan.buetow.org:zdata.key
+*r--------  1 root wheel 32 May 25 13:07 f2.lan.buetow.org:zdata.key
+````
+
+After creation, these are copied to the other two nodes, `f1` and `f2`, into the `/keys` partition (I won't provide the commands here; create a tarball, copy it over, and extract it on the destination nodes).
+
+### Configuring `zdata` ZFS pool encryption
+
+Let's encrypt our `zdata` ZFS pool. We are not encrypting the whole pool, but everything within the `zdata/enc` data set:
+
+```sh
+paul@f0:/keys % doas zfs create -o encryption=on -o keyformat=raw -o \
+  keylocation=file:///keys/`hostname`:zdata.key zdata/enc
+paul@f0:/ % zfs list | grep zdata
+zdata                                          836K   899G    96K  /data
+zdata/enc                                      200K   899G   200K  /data/enc
+
+paul@f0:/keys % zfs get all zdata/enc | grep -E -i '(encryption|key)'
+zdata/enc  encryption            aes-256-gcm                               -
+zdata/enc  keylocation           file:///keys/f0.lan.buetow.org:zdata.key  local
+zdata/enc  keyformat             raw                                       -
+zdata/enc  encryptionroot        zdata/enc                                 -
+zdata/enc  keystatus             available                                 -
+````
+
+All future data sets within `zdata/enc` will inherit the same encryption key.
+
+### Migrating Bhyve VMs to an encrypted `bhyve` ZFS volume
+
+We set up Bhyve VMs in a previous blog post. Their ZFS data sets rely on `zroot`, which is the default ZFS pool on the internal 512GB NVME drive. They aren't encrypted yet, so we encrypt the VM data sets as well now. To do so, we first shut down the VMs on all three nodes:
+
+```sh
+paul@f0:/keys % doas vm stop rocky
+Sending ACPI shutdown to rocky
+
+paul@f0:/keys % doas vm list
+NAME     DATASTORE  LOADER     CPU  MEMORY  VNC  AUTO     STATE
+rocky    default    uefi       4    14G     -    Yes [1]  Stopped
+```
+
+After this, we rename the unencrypted data set to `_old`, create a new encrypted data set, and also snapshot it as `@hamburger`.
+  
+```sh
+paul@f0:/keys % doas zfs rename zroot/bhyve zroot/bhyve_old
+paul@f0:/keys % doas zfs set mountpoint=/mnt zroot/bhyve_old
+paul@f0:/keys % doas zfs snapshot zroot/bhyve_old/rocky@hamburger
+
+paul@f0:/keys % doas zfs create -o encryption=on -o keyformat=raw -o \
+  keylocation=file:///keys/`hostname`:bhyve.key zroot/bhyve
+paul@f0:/keys % doas zfs set mountpoint=/zroot/bhyve zroot/bhyve
+paul@f0:/keys % doas zfs set mountpoint=/zroot/bhyve/rocky zroot/bhyve/rocky
+```
+
+Once done, we import the snapshot into the encrypted dataset and also copy some other metadata files from `vm-bhyve` back over.
+
+```
+paul@f0:/keys % doas zfs send zroot/bhyve_old/rocky@hamburger | \
+  doas zfs recv zroot/bhyve/rocky
+paul@f0:/keys % doas cp -Rp /mnt/.config /zroot/bhyve/
+paul@f0:/keys % doas cp -Rp /mnt/.img /zroot/bhyve/
+paul@f0:/keys % doas cp -Rp /mnt/.templates /zroot/bhyve/
+paul@f0:/keys % doas cp -Rp /mnt/.iso /zroot/bhyve/
+```
+
+We also have to make encrypted ZFS data sets mount automatically on boot:
+
+```sh
+paul@f0:/keys % doas sysrc zfskeys_enable=YES
+zfskeys_enable:  -> YES
+paul@f0:/keys % doas vm init
+paul@f0:/keys % doas reboot
+.
+.
+.
+paul@f0:~ % doas vm list
+paul@f0:~ % doas vm list
+NAME     DATASTORE  LOADER     CPU  MEMORY  VNC           AUTO     STATE
+rocky    default    uefi       4    14G     0.0.0.0:5900  Yes [1]  Running (2265)
+```
+
+As you can see, the VM is running. This means the encrypted `zroot/bhyve` was mounted successfully after the reboot! Now we can destroy the old, unencrypted, and now unused bhyve dataset:
+
+```sh
+paul@f0:~ % doas zfs destroy -R zroot/bhyve_old
+```
+
+To verify once again that `zroot/bhyve` and `zroot/bhyve/rocky` are now both encrypted, we run:
+  
+```sh
+paul@f0:~ % zfs get all zroot/bhyve | grep -E '(encryption|key)'
+zroot/bhyve  encryption            aes-256-gcm                               -
+zroot/bhyve  keylocation           file:///keys/f0.lan.buetow.org:bhyve.key  local
+zroot/bhyve  keyformat             raw                                       -
+zroot/bhyve  encryptionroot        zroot/bhyve                               -
+zroot/bhyve  keystatus             available                                 -
+
+paul@f0:~ % zfs get all zroot/bhyve/rocky | grep -E '(encryption|key)'
+zroot/bhyve/rocky  encryption            aes-256-gcm            -
+zroot/bhyve/rocky  keylocation           none                   default
+zroot/bhyve/rocky  keyformat             raw                    -
+zroot/bhyve/rocky  encryptionroot        zroot/bhyve            -
+zroot/bhyve/rocky  keystatus             available              -
+```
+
+## ZFS Replication with `zrepl`
+
+Data replication is the cornerstone of high availability. While CARP handles IP failover (see later in this post), we need continuous data replication to ensure the backup server has current data when it becomes active. Without replication, failover would result in data loss or require shared storage (like iSCSI), which introduces a single point of failure.
+
+### Understanding Replication Requirements
+
+Our storage system has different replication needs:
+
+* NFS data (`/data/nfs/k3svolumes`): Soon, it will contain active Kubernetes persistent volumes. Needs frequent replication (every minute) to minimise data loss during failover.
+* VM data (`/zroot/bhyve/fedora`): Contains VM images that change less frequently. Can tolerate longer replication intervals (every 10 minutes).
+
+The 1-minute replication window is perfectly acceptable for my personal use cases. This isn't a high-frequency trading system or a real-time database—it's storage for personal projects, development work, and home lab experiments. Losing at most 1 minute of work in a disaster scenario is a reasonable trade-off for the reliability and simplicity of snapshot-based replication. Additionally, in the case of a "1 minute of data loss," I would likely still have the data available on the client side.
+
+Why use `zrepl` instead of HAST? While HAST (Highly Available Storage) is FreeBSD's native solution for high-availability storage and supports synchronous replication—thus eliminating the mentioned 1-minute window—I've chosen `zrepl` for several important reasons:
+
+* HAST can cause ZFS corruption: HAST operates at the block level and doesn't understand ZFS's transactional semantics. During failover, in-flight transactions can lead to corrupted zpools. I've experienced this firsthand (I am confident I have configured something wrong) - the automatic failover would trigger while ZFS was still writing, resulting in an unmountable pool.
+* ZFS-aware replication: `zrepl` understands ZFS datasets and snapshots. It replicates at the dataset level, ensuring each snapshot is a consistent point-in-time copy. This is fundamentally safer than block-level replication.
+* Snapshot history: With `zrepl`, you get multiple recovery points (every minute for NFS data in our setup). If corruption occurs, you can roll back to any previous snapshot. HAST only gives you the current state.
+* Easier recovery: When something goes wrong with `zrepl`, you still have intact snapshots on both sides. With HAST, a corrupted primary often means a corrupted secondary as well.
+
+=> https://wiki.freebsd.org/HighlyAvailableStorage FreeBSD HAST
+
+### Installing `zrepl`
+
+First, install `zrepl` on both hosts involved (we will replicate data from `f0` to `f1`):
+
+```sh
+paul@f0:~ % doas pkg install -y zrepl
+```
+
+Then, we verify the pools and datasets on both hosts:
+
+```sh
+# On f0
+paul@f0:~ % doas zpool list
+NAME    SIZE  ALLOC   FREE  CKPOINT  EXPANDSZ   FRAG    CAP  DEDUP    HEALTH  ALTROOT
+zdata   928G  1.03M   928G        -         -     0%     0%  1.00x    ONLINE  -
+zroot   472G  26.7G   445G        -         -     0%     5%  1.00x    ONLINE  -
+
+paul@f0:~ % doas zfs list -r zdata/enc
+NAME        USED  AVAIL  REFER  MOUNTPOINT
+zdata/enc   200K   899G   200K  /data/enc
+
+# On f1
+paul@f1:~ % doas zpool list
+NAME    SIZE  ALLOC   FREE  CKPOINT  EXPANDSZ   FRAG    CAP  DEDUP    HEALTH  ALTROOT
+zdata   928G   956K   928G        -         -     0%     0%  1.00x    ONLINE  -
+zroot   472G  11.7G   460G        -         -     0%     2%  1.00x    ONLINE  -
+
+paul@f1:~ % doas zfs list -r zdata/enc
+NAME        USED  AVAIL  REFER  MOUNTPOINT
+zdata/enc   200K   899G   200K  /data/enc
+```
+
+Since we have a WireGuard tunnel between `f0` and f1, we'll use TCP transport over the secure tunnel instead of SSH. First, check the WireGuard IP addresses:
+
+```sh
+# Check WireGuard interface IPs
+paul@f0:~ % ifconfig wg0 | grep inet
+	inet 192.168.2.130 netmask 0xffffff00
+
+paul@f1:~ % ifconfig wg0 | grep inet
+	inet 192.168.2.131 netmask 0xffffff00
+```
+
+Let's create a dedicated dataset for NFS data that will be replicated:
+
+```sh
+# Create the nfsdata dataset that will hold all data exposed via NFS
+paul@f0:~ % doas zfs create zdata/enc/nfsdata
+```
+
+Afterwards, we create the `zrepl` configuration on `f0`:
+
+```sh
+paul@f0:~ % doas tee /usr/local/etc/zrepl/zrepl.yml <<'EOF'
+global:
+  logging:
+    - type: stdout
+      level: info
+      format: human
+
+jobs:
+  - name: f0_to_f1_nfsdata
+    type: push
+    connect:
+      type: tcp
+      address: "192.168.2.131:8888"
+    filesystems:
+      "zdata/enc/nfsdata": true
+    send:
+      encrypted: true
+    snapshotting:
+      type: periodic
+      prefix: zrepl_
+      interval: 1m
+    pruning:
+      keep_sender:
+        - type: last_n
+          count: 10
+      keep_receiver:
+        - type: last_n
+          count: 10
+
+  - name: f0_to_f1_fedora
+    type: push
+    connect:
+      type: tcp
+      address: "192.168.2.131:8888"
+    filesystems:
+      "zroot/bhyve/fedora": true
+    send:
+      encrypted: true
+    snapshotting:
+      type: periodic
+      prefix: zrepl_
+      interval: 10m
+    pruning:
+      keep_sender:
+        - type: last_n
+          count: 10
+      keep_receiver:
+        - type: last_n
+          count: 10
+EOF
+```
+
+ We're using two separate replication jobs with different intervals:
+
+* `f0_to_f1_nfsdata`: Replicates NFS data every minute for faster failover recovery
+* `f0_to_f1_fedora`: Replicates Fedora VM every ten minutes (less critical)
+
+The Fedora VM is only used for development purposes, so it doesn't require as frequent replication as the NFS data. It's off-topic to this blog series, but it showcases, hows `zrepl`'s flexibility in handling different datasets with varying replication needs.
+
+Furthermore:
+
+* We're specifically replicating `zdata/enc/nfsdata` instead of the entire `zdata/enc` dataset. This dedicated dataset will contain all the data we later want to expose via NFS, keeping a clear separation between replicated NFS data and other local encrypted data.
+* The `send: encrypted: false` option turns off ZFS native encryption for the replication stream. Since we're using a WireGuard tunnel between `f0` and `f1`, the data is already encrypted in transit. Disabling ZFS stream encryption reduces CPU overhead and improves replication performance.
+
+### Configuring `zrepl` on `f1` (sink)
+
+On `f1` (the sink, meaning it's the node receiving the replication data), we configure `zrepl` to receive the data as follows:
+
+```sh
+# First, create a dedicated sink dataset
+paul@f1:~ % doas zfs create zdata/sink
+
+paul@f1:~ % doas tee /usr/local/etc/zrepl/zrepl.yml <<'EOF'
+global:
+  logging:
+    - type: stdout
+      level: info
+      format: human
+
+jobs:
+  - name: sink
+    type: sink
+    serve:
+      type: tcp
+      listen: "192.168.2.131:8888"
+      clients:
+        "192.168.2.130": "f0"
+    recv:
+      placeholder:
+        encryption: inherit
+    root_fs: "zdata/sink"
+EOF
+```
+
+### Enabling and starting `zrepl` services
+
+We then enable and start `zrepl` on both hosts via:
+
+```sh
+# On f0
+paul@f0:~ % doas sysrc zrepl_enable=YES
+zrepl_enable:  -> YES
+paul@f0:~ % doas service `zrepl` start
+Starting zrepl.
+
+# On f1
+paul@f1:~ % doas sysrc zrepl_enable=YES
+zrepl_enable:  -> YES
+paul@f1:~ % doas service `zrepl` start
+Starting zrepl.
+```
+
+To check the replication status, we run:
+
+```sh
+# On f0, check `zrepl` status (use raw mode for non-tty)
+paul@f0:~ % doas pkg install jq
+paul@f0:~ % doas zrepl status --mode raw | grep -A2 "Replication" | jq .
+"Replication":{"StartAt":"2025-07-01T22:31:48.712143123+03:00"...
+
+# Check if services are running
+paul@f0:~ % doas service zrepl status
+zrepl is running as pid 2649.
+
+paul@f1:~ % doas service zrepl status
+zrepl is running as pid 2574.
+
+# Check for `zrepl` snapshots on source
+paul@f0:~ % doas zfs list -t snapshot -r zdata/enc | grep zrepl
+zdata/enc@zrepl_20250701_193148_000    0B      -   176K  -
+
+# On f1, verify the replicated datasets  
+paul@f1:~ % doas zfs list -r zdata | grep f0
+zdata/f0             576K   899G   200K  none
+zdata/f0/zdata       376K   899G   200K  none
+zdata/f0/zdata/enc   176K   899G   176K  none
+
+# Check replicated snapshots on f1
+paul@f1:~ % doas zfs list -t snapshot -r zdata | grep zrepl
+zdata/f0/zdata/enc@zrepl_20250701_193148_000     0B      -   176K  -
+zdata/f0/zdata/enc@zrepl_20250701_194148_000     0B      -   176K  -
+.
+.
+.
+```
+
+### Monitoring replication
+
+You can monitor the replication progress with:
+
+```sh
+paul@f0:~ % doas zrepl status
+```
+
+=> ./f3s-kubernetes-with-freebsd-part-6/zrepl.png zrepl status
+
+With this setup, both `zdata/enc/nfsdata` and `zroot/bhyve/fedora` on `f0` will be automatically replicated to `f1` every 1 minute (or 10 minutes in the case of the Fedora VM), with encrypted snapshots preserved on both sides. The pruning policy ensures that we keep the last 10 snapshots while managing disk space efficiently.
+
+The replicated data appears on `f1` under `zdata/sink/` with the source host and dataset hierarchy preserved:
+
+* `zdata/enc/nfsdata` → `zdata/sink/f0/zdata/enc/nfsdata`
+* `zroot/bhyve/fedora` → `zdata/sink/f0/zroot/bhyve/fedora`
+
+This is by design - `zrepl` preserves the complete path from the source to ensure there are no conflicts when replicating from multiple sources.
+
+### Verifying replication after reboot
+
+The `zrepl` service is configured to start automatically at boot. After rebooting both hosts:
+
+```sh
+paul@f0:~ % uptime
+11:17PM  up 1 min, 0 users, load averages: 0.16, 0.06, 0.02
+
+paul@f0:~ % doas service `zrepl` status
+zrepl is running as pid 2366.
+
+paul@f1:~ % doas service `zrepl` status
+zrepl is running as pid 2309.
+
+# Check that new snapshots are being created and replicated
+paul@f0:~ % doas zfs list -t snapshot | grep `zrepl` | tail -2
+zdata/enc/nfsdata@zrepl_20250701_202530_000                0B      -   200K  -
+zroot/bhyve/fedora@zrepl_20250701_202530_000               0B      -  2.97G  -
+.
+.
+.
+
+paul@f1:~ % doas zfs list -t snapshot -r zdata/sink | grep 202530
+zdata/sink/f0/zdata/enc/nfsdata@zrepl_20250701_202530_000      0B      -   176K  -
+zdata/sink/f0/zroot/bhyve/fedora@zrepl_20250701_202530_000     0B      -  2.97G  -
+.
+.
+.
+```
+
+The timestamps confirm that replication resumed automatically after the reboot, ensuring continuous data protection. We can also write a test file to the NFS data directory on `f0` and verify whether it appears on `f1` after a minute.
+
+### Understanding Failover Limitations and Design Decisions
+
+Our system intentionally fails over to a read-only copy of the replica in the event of the primary's failure. This is due to the nature of `zrepl`, which only replicates data in one direction. If we mount the data set on the sink node in read-write mode, it would cause the ZFS dataset to diverge from the original, and the replication would break. It can still be mounted read-write on the sink node in case of a genuine issue on the primary node, but that step is left intentionally manual. Therefore, we don't need to fix the replication later on manually.
+
+So in summary:
+
+* Split-brain prevention: Automatic failover to a read-write copy can cause both nodes to become active simultaneously if network communication fails. This leads to data divergence that's extremely difficult to resolve.
+* False positive protection: Temporary network issues or high load can trigger unwanted failovers. Manual intervention ensures that failovers occur only when truly necessary.
+* Data integrity over availability: For storage systems, data consistency is paramount. A few minutes of downtime is preferable to data corruption in this specific use case.
+* Simplified recovery: With manual failover, you always know which dataset is authoritative, making recovery more straightforward.
+
+### Mounting the NFS datasets
+
+To make the NFS data accessible on both nodes, we need to mount it. On `f0`, this is straightforward:
+
+```sh
+# On f0 - set mountpoint for the primary nfsdata
+paul@f0:~ % doas zfs set mountpoint=/data/nfs zdata/enc/nfsdata
+paul@f0:~ % doas mkdir -p /data/nfs
+
+# Verify it's mounted
+paul@f0:~ % df -h /data/nfs
+Filesystem           Size    Used   Avail Capacity  Mounted on
+zdata/enc/nfsdata    899G    204K    899G     0%    /data/nfs
+```
+
+On `f1`, we need to handle the encryption key and mount the standby copy:
+
+```sh
+# On f1 - first check encryption status
+paul@f1:~ % doas zfs get keystatus zdata/sink/f0/zdata/enc/nfsdata
+NAME                             PROPERTY   VALUE        SOURCE
+zdata/sink/f0/zdata/enc/nfsdata  keystatus  unavailable  -
+
+# Load the encryption key (using f0's key stored on the USB)
+paul@f1:~ % doas zfs load-key -L file:///keys/f0.lan.buetow.org:zdata.key \
+    zdata/sink/f0/zdata/enc/nfsdata
+
+# Set mountpoint and mount (same path as f0 for easier failover)
+paul@f1:~ % doas mkdir -p /data/nfs
+paul@f1:~ % doas zfs set mountpoint=/data/nfs zdata/sink/f0/zdata/enc/nfsdata
+paul@f1:~ % doas zfs mount zdata/sink/f0/zdata/enc/nfsdata
+
+# Make it read-only to prevent accidental writes that would break replication
+paul@f1:~ % doas zfs set readonly=on zdata/sink/f0/zdata/enc/nfsdata
+
+# Verify
+paul@f1:~ % df -h /data/nfs
+Filesystem                         Size    Used   Avail Capacity  Mounted on
+zdata/sink/f0/zdata/enc/nfsdata    896G    204K    896G     0%    /data/nfs
+```
+
+Note: The dataset is mounted at the same path (`/data/nfs`) on both hosts to simplify failover procedures. The dataset on `f1` is set to `readonly=on` to prevent accidental modifications, which, as mentioned earlier, would break replication. If we did, replication from `f0` to `f1` would fail like this:
+
+> cannot receive incremental stream: destination zdata/sink/f0/zdata/enc/nfsdata has been modified since most recent snapshot 
+
+To fix a broken replication after accidental writes, we can do:
+
+```sh
+# Option 1: Rollback to the last common snapshot (loses local changes)
+paul@f1:~ % doas zfs rollback zdata/sink/f0/zdata/enc/nfsdata@zrepl_20250701_204054_000
+
+# Option 2: Make it read-only to prevent accidents again
+paul@f1:~ % doas zfs set readonly=on zdata/sink/f0/zdata/enc/nfsdata
+```
+
+And replication should work again!
+
+### Troubleshooting: Files not appearing in replication
+
+If you write files to `/data/nfs/` on `f0` but they don't appear on `f1`, check if the dataset is mounted on `f0`?
+
+```sh
+paul@f0:~ % doas zfs list -o name,mountpoint,mounted | grep nfsdata
+zdata/enc/nfsdata                             /data/nfs             yes
+```
+
+If it shows `no`, the dataset isn't mounted! This means files are being written to the root filesystem, not ZFS. Next, we should check whether the encryption key is loaded:
+
+```sh
+paul@f0:~ % doas zfs get keystatus zdata/enc/nfsdata
+NAME               PROPERTY   VALUE        SOURCE
+zdata/enc/nfsdata  keystatus  available    -
+# If "unavailable", load the key:
+paul@f0:~ % doas zfs load-key -L file:///keys/f0.lan.buetow.org:zdata.key zdata/enc/nfsdata
+paul@f0:~ % doas zfs mount zdata/enc/nfsdata
+```
+
+You can also verify that files are in the snapshot (not just the directory):
+
+```sh
+paul@f0:~ % ls -la /data/nfs/.zfs/snapshot/zrepl_*/
+```
+
+This issue commonly occurs after a reboot if the encryption keys aren't configured to load automatically.
+
+### Configuring automatic key loading on boot
+
+To ensure all additional encrypted datasets are mounted automatically after reboot as well, we do:
+
+```sh
+# On f0 - configure all encrypted datasets
+paul@f0:~ % doas sysrc zfskeys_enable=YES
+zfskeys_enable: YES -> YES
+paul@f0:~ % doas sysrc zfskeys_datasets="zdata/enc zdata/enc/nfsdata zroot/bhyve"
+zfskeys_datasets:  -> zdata/enc zdata/enc/nfsdata zroot/bhyve
+
+# Set correct key locations for all datasets
+paul@f0:~ % doas zfs set keylocation=file:///keys/f0.lan.buetow.org:zdata.key zdata/enc/nfsdata
+
+# On f1 - include the replicated dataset
+paul@f1:~ % doas sysrc zfskeys_enable=YES
+zfskeys_enable: YES -> YES
+paul@f1:~ % doas sysrc zfskeys_datasets="zdata/enc zroot/bhyve zdata/sink/f0/zdata/enc/nfsdata"
+zfskeys_datasets:  -> zdata/enc zroot/bhyve zdata/sink/f0/zdata/enc/nfsdata
+
+# Set key location for replicated dataset
+paul@f1:~ % doas zfs set keylocation=file:///keys/f0.lan.buetow.org:zdata.key zdata/sink/f0/zdata/enc/nfsdata
+```
+
+Important notes:
+
+* Each encryption root needs its own key load entry
+* The replicated dataset on `f1` uses the same encryption key as the source on `f0`
+* Always verify datasets are mounted after reboot with `zfs list -o name,mounted`
+* Critical: Always ensure the replicated dataset on `f1` remains read-only with `doas zfs set readonly=on zdata/sink/f0/zdata/enc/nfsdata`
+
+## CARP (Common Address Redundancy Protocol)
+
+High availability is crucial for storage systems. If the storage server goes down, all NFS clients (which will also be Kubernetes pods later on in this series) lose access to their persistent data. CARP provides a solution by creating a virtual IP address that automatically migrates to a different server during failures. This means that clients point to that VIP for NFS mounts and are always contacting the current primary node.
+
+### How CARP Works
+
+In our case, CARP allows two hosts (`f0` and `f1`) to share a virtual IP address (VIP). The hosts communicate using multicast to elect a MASTER, while the other remain as BACKUP. When the MASTER fails, the BACKUP automatically promotes itself, and the VIP is reassigned to the new MASTER. This happens within seconds.
+
+Key benefits for our storage system:
+
+* Automatic failover: No manual intervention is required for basic failures, although there are a few limitations. The backup will have read-only access to the available data by default, as we have already learned.
+* Transparent to clients: Pods continue using the same IP address
+* Works with `stunnel`: Behind the VIP, there will be a `stunnel` process running, which ensures encrypted connections follow the active server.
+
+=> https://docs-archive.freebsd.org/doc/13.0-RELEASE/usr/local/share/doc/freebsd/en/books/handbook/carp.html FreeBSD CARP
+=> https://www.stunnel.org/ Stunnel
+
+### Configuring CARP
+
+First, we add the CARP configuration to `/etc/rc.conf` on both `f0` and `f1`:
+
+```sh
+# The virtual IP 192.168.1.138 will float between f0 and f1
+ifconfig_re0_alias0="inet vhid 1 pass testpass alias 192.168.1.138/32"
+```
+
+Whereas:
+
+* `vhid 1`: Virtual Host ID - must match on all CARP members
+* `pass testpass`: Password for CARP authentication (if you follow this, use a different password!)
+* `alias 192.168.1.138/32`: The virtual IP address with a /32 netmask
+
+Next, update `/etc/hosts` on all nodes (n0, n1, n2, r0, r1, r2) to resolve the VIP hostname:
+
+```
+192.168.1.138 f3s-storage-ha f3s-storage-ha.lan f3s-storage-ha.lan.buetow.org
+```
+
+This allows clients to connect to `f3s-storage-ha` regardless of which physical server is currently the MASTER.
+
+### CARP State Change Notifications
+
+To correctly manage services during failover, we need to detect CARP state changes. FreeBSD's devd system can notify us when CARP transitions between MASTER and BACKUP states.
+
+Add this to `/etc/devd.conf` on both `f0` and `f1`:
+
+```sh
+paul@f0:~ % cat <<END | doas tee -a /etc/devd.conf
+notify 0 {
+        match "system"          "CARP";
+        match "subsystem"       "[0-9]+@[0-9a-z.]+";
+        match "type"            "(MASTER|BACKUP)";
+        action "/usr/local/bin/carpcontrol.sh $subsystem $type";
+};
+END
+
+paul@f0:~ % doas service devd restart
+```
+
+Next, we create the CARP control script that will restart stunnel when the CARP state changes:
+
+```sh
+paul@f0:~ % doas tee /usr/local/bin/carpcontrol.sh <<'EOF'
+#!/bin/sh
+# CARP state change control script
+
+case "$1" in
+    MASTER)
+        logger "CARP state changed to MASTER, starting services"
+        ;;
+    BACKUP)
+        logger "CARP state changed to BACKUP, stopping services"
+        ;;
+    *)
+        logger "CARP state changed to $1 (unhandled)"
+        ;;
+esac
+EOF
+
+paul@f0:~ % doas chmod +x /usr/local/bin/carpcontrol.sh
+
+# Copy the same script to f1
+paul@f0:~ % scp /usr/local/bin/carpcontrol.sh f1:/tmp/
+paul@f1:~ % doas mv /tmp/carpcontrol.sh /usr/local/bin/
+paul@f1:~ % doas chmod +x /usr/local/bin/carpcontrol.sh
+```
+
+Note that `carpcontrol.sh` doesn't do anything useful yet. We will provide more details (including starting and stopping services upon failover) later in this blog post.
+
+To enable CARP in `/boot/loader.conf`, run:
+
+```sh
+paul@f0:~ % echo 'carp_load="YES"' | doas tee -a /boot/loader.conf
+carp_load="YES"
+paul@f1:~ % echo 'carp_load="YES"' | doas tee -a /boot/loader.conf  
+carp_load="YES"
+```
+
+Then reboot both hosts or run `doas kldload carp` to load the module immediately. 
+
+## NFS Server Configuration
+
+With ZFS replication in place, we can now set up NFS servers on both `f0` and `f1` to export the replicated data. Since native NFS over TLS (RFC 9289) has compatibility issues between Linux and FreeBSD (not digging into the details here, but I couldn't get it to work), we'll use stunnel to provide encryption.
+
+### Setting up NFS on `f0` (Primary)
+
+First, enable the NFS services in rc.conf:
+
+```sh
+paul@f0:~ % doas sysrc nfs_server_enable=YES
+nfs_server_enable: YES -> YES
+paul@f0:~ % doas sysrc nfsv4_server_enable=YES
+nfsv4_server_enable: YES -> YES
+paul@f0:~ % doas sysrc nfsuserd_enable=YES
+nfsuserd_enable: YES -> YES
+paul@f0:~ % doas sysrc mountd_enable=YES
+mountd_enable: NO -> YES
+paul@f0:~ % doas sysrc rpcbind_enable=YES
+rpcbind_enable: NO -> YES
+```
+
+And we also create a dedicated directory for Kubernetes volumes:
+
+```sh
+# First, ensure the dataset is mounted
+paul@f0:~ % doas zfs get mounted zdata/enc/nfsdata
+NAME               PROPERTY  VALUE    SOURCE
+zdata/enc/nfsdata  mounted   yes      -
+
+# Create the k3svolumes directory
+paul@f0:~ % doas mkdir -p /data/nfs/k3svolumes
+paul@f0:~ % doas chmod 755 /data/nfs/k3svolumes
+```
+
+We also create the `/etc/exports` file. Since we're using stunnel for encryption, ALL clients must connect through stunnel, which appears as localhost (`127.0.0.1`) to the NFS server:
+
+```sh
+paul@f0:~ % doas tee /etc/exports <<'EOF'
+V4: /data/nfs -sec=sys
+/data/nfs -alldirs -maproot=root -network 127.0.0.1 -mask 255.255.255.255
+EOF
+```
+
+The exports configuration:
+
+* `V4: /data/nfs -sec=sys`: Sets the NFSv4 root directory to /data/nfs
+* `-maproot=root`: Maps root user from client to root on server
+* `-network 127.0.0.1`: Only accepts connections from localhost (`stunnel`)
+
+To start the NFS services, we run:
+
+```sh
+paul@f0:~ % doas service rpcbind start
+Starting rpcbind.
+paul@f0:~ % doas service mountd start
+Starting mountd.
+paul@f0:~ % doas service nfsd start
+Starting nfsd.
+paul@f0:~ % doas service nfsuserd start
+Starting nfsuserd.
+```
+
+### Configuring Stunnel for NFS Encryption with CARP Failover
+
+Using stunnel with client certificate authentication for NFS encryption provides several advantages:
+
+* Compatibility: Works with any NFS version and between different operating systems
+* Strong encryption: Uses TLS/SSL with configurable cipher suites
+* Transparent: Applications don't need modification, encryption happens at the transport layer
+* Performance: Minimal overhead (~2% in benchmarks)
+* Flexibility: Can encrypt any TCP-based protocol, not just NFS
+* Strong Authentication: Client certificates provide cryptographic proof of identity
+* Access Control: Only clients with valid certificates signed by your CA can connect
+* Certificate Revocation: You can revoke access by removing certificates from the CA
+
+Stunnel integrates seamlessly with our CARP setup:
+
+```
+                    CARP VIP (192.168.1.138)
+                           |
+    f0 (MASTER) ←---------→|←---------→ f1 (BACKUP)
+    stunnel:2323           |           stunnel:stopped
+    nfsd:2049              |           nfsd:stopped
+                           |
+                    Clients connect here
+```
+
+The key insight is that stunnel binds to the CARP VIP. When CARP fails over, the VIP is moved to the new master, and stunnel starts there automatically. Clients maintain their connection to the same IP throughout.
+
+### Creating a Certificate Authority for Client Authentication
+
+First, create a CA to sign both server and client certificates:
+
+```sh
+# On f0 - Create CA
+paul@f0:~ % doas mkdir -p /usr/local/etc/stunnel/ca
+paul@f0:~ % cd /usr/local/etc/stunnel/ca
+paul@f0:~ % doas openssl genrsa -out ca-key.pem 4096
+paul@f0:~ % doas openssl req -new -x509 -days 3650 -key ca-key.pem -out ca-cert.pem \
+  -subj '/C=US/ST=State/L=City/O=F3S Storage/CN=F3S Stunnel CA'
+
+# Create server certificate
+paul@f0:~ % cd /usr/local/etc/stunnel
+paul@f0:~ % doas openssl genrsa -out server-key.pem 4096
+paul@f0:~ % doas openssl req -new -key server-key.pem -out server.csr \
+  -subj '/C=US/ST=State/L=City/O=F3S Storage/CN=f3s-storage-ha.lan'
+paul@f0:~ % doas openssl x509 -req -days 3650 -in server.csr -CA ca/ca-cert.pem \
+  -CAkey ca/ca-key.pem -CAcreateserial -out server-cert.pem
+
+# Create client certificates for authorised clients
+paul@f0:~ % cd /usr/local/etc/stunnel/ca
+paul@f0:~ % doas sh -c 'for client in r0 r1 r2 earth; do 
+  openssl genrsa -out ${client}-key.pem 4096
+  openssl req -new -key ${client}-key.pem -out ${client}.csr \
+    -subj "/C=US/ST=State/L=City/O=F3S Storage/CN=${client}.lan.buetow.org"
+  openssl x509 -req -days 3650 -in ${client}.csr -CA ca-cert.pem \
+    -CAkey ca-key.pem -CAcreateserial -out ${client}-cert.pem
+done'
+```
+
+### Install and Configure Stunnel on `f0`
+
+```sh
+# Install stunnel
+paul@f0:~ % doas pkg install -y stunnel
+
+# Configure stunnel server with client certificate authentication
+paul@f0:~ % doas tee /usr/local/etc/stunnel/stunnel.conf <<'EOF'
+cert = /usr/local/etc/stunnel/server-cert.pem
+key = /usr/local/etc/stunnel/server-key.pem
+
+setuid = stunnel
+setgid = stunnel
+
+[nfs-tls]
+accept = 192.168.1.138:2323
+connect = 127.0.0.1:2049
+CAfile = /usr/local/etc/stunnel/ca/ca-cert.pem
+verify = 2
+requireCert = yes
+EOF
+
+# Enable and start stunnel
+paul@f0:~ % doas sysrc stunnel_enable=YES
+stunnel_enable:  -> YES
+paul@f0:~ % doas service stunnel start
+Starting stunnel.
+
+# Restart stunnel to apply the CARP VIP binding
+paul@f0:~ % doas service stunnel restart
+Stopping stunnel.
+Starting stunnel.
+```
+
+The configuration includes:
+
+* `verify = 2`: Verify client certificate and fail if not provided
+* `requireCert = yes`: Client must present a valid certificate
+* `CAfile`: Path to the CA certificate that signed the client certificates
+
+### Setting up NFS on `f1` (Standby)
+
+Repeat the same configuration on `f1`:
+
+```sh
+paul@f1:~ % doas sysrc nfs_server_enable=YES
+nfs_server_enable: NO -> YES
+paul@f1:~ % doas sysrc nfsv4_server_enable=YES
+nfsv4_server_enable: NO -> YES
+paul@f1:~ % doas sysrc nfsuserd_enable=YES
+nfsuserd_enable: NO -> YES
+paul@f1:~ % doas sysrc mountd_enable=YES
+mountd_enable: NO -> YES
+paul@f1:~ % doas sysrc rpcbind_enable=YES
+rpcbind_enable: NO -> YES
+
+paul@f1:~ % doas tee /etc/exports <<'EOF'