Add ZFS management role: scrub scheduling and pool monitoring (#18)

- New zfs role with cron-based scrub scheduling for Linux and FreeBSD
- Weekly Sunday scrubs at noon (matching existing manual crons)
- Add zfs_hosts inventory group with london-a and london-b
- Configure zfs_pools per host: zroot (london-a), hdd (london-b)
- Add Prometheus alert rules for degraded/faulted/offline pools
- Add zfs.yml playbook for targeted deploys

Captures the previously untracked scrub cron on london-a and
re-enables the commented-out scrub on london-b.

Refs: PESO-93

ansible/inventory/host_vars/london-a.yml

@@ -4,3 +4,6 @@ host_description: "Monitoring stack (Prometheus, Grafana)"
 host_location: "London"
 ansible_python_interpreter: /usr/local/bin/python3
 grafana_provisioning_dir: /usr/local/share/grafana/conf/provisioning
+
+zfs_pools:
+  - zroot

ansible/inventory/host_vars/london-b.yml

@@ -12,6 +12,9 @@ docker_services:
   - smartctl-exporter
   - plex-exporter
 
+zfs_pools:
+  - hdd
+
 common_ufw_allowed_ports:
   - {port: 32400, proto: tcp, comment: "Plex Media Server"}
   - {port: 6881, proto: tcp, comment: "BitTorrent"}

ansible/inventory/hosts.ini

@@ -13,6 +13,10 @@ nuremberg-a  ansible_host=100.117.235.28
 [freebsd]
 london-a     ansible_host=100.122.219.41
 
+[zfs_hosts]
+london-a
+london-b
+
 [docker_hosts]
 helsinki-a
 london-b

ansible/playbooks/zfs.yml

@@ -0,0 +1,9 @@
+---
+# Deploy ZFS management (scrub scheduling, monitoring).
+# Usage: ansible-playbook playbooks/zfs.yml
+#        ansible-playbook playbooks/zfs.yml --check --diff
+
+- name: "ZFS management"
+  hosts: zfs_hosts
+  roles:
+    - zfs

ansible/roles/zfs/defaults/main.yml

@@ -0,0 +1,15 @@
+---
+# ZFS management defaults
+
+# List of ZFS pools to manage scrubs for.
+# Override per-host in host_vars.
+zfs_pools: []
+
+# Scrub schedule (cron format).
+# Default: weekly on Sunday at noon.
+zfs_scrub_weekday: "0"    # 0 = Sunday
+zfs_scrub_hour: "12"
+zfs_scrub_minute: "0"
+
+# Whether to enable ZFS scrub scheduling.
+zfs_scrub_enabled: true

ansible/roles/zfs/tasks/main.yml

@@ -0,0 +1,29 @@
+---
+# ZFS management: scrub scheduling, pool monitoring.
+# Supports both Linux (systemd timers / cron) and FreeBSD (crontab).
+
+- name: "ZFS scrub scheduling (Linux)"
+  when: ansible_os_family != "FreeBSD" and zfs_scrub_enabled
+  block:
+    - name: Install ZFS scrub cron jobs (Linux)
+      ansible.builtin.cron:
+        name: "ZFS scrub {{ item }}"
+        minute: "{{ zfs_scrub_minute }}"
+        hour: "{{ zfs_scrub_hour }}"
+        weekday: "{{ zfs_scrub_weekday }}"
+        job: "/sbin/zpool scrub {{ item }}"
+        user: root
+      loop: "{{ zfs_pools }}"
+
+- name: "ZFS scrub scheduling (FreeBSD)"
+  when: ansible_os_family == "FreeBSD" and zfs_scrub_enabled
+  block:
+    - name: Install ZFS scrub cron jobs (FreeBSD)
+      ansible.builtin.cron:
+        name: "ZFS scrub {{ item }}"
+        minute: "{{ zfs_scrub_minute }}"
+        hour: "{{ zfs_scrub_hour }}"
+        weekday: "{{ zfs_scrub_weekday }}"
+        job: "/sbin/zpool scrub {{ item }}"
+        user: root
+      loop: "{{ zfs_pools }}"

ansible/services/prometheus/rules/zfs.rules

@@ -0,0 +1,29 @@
+groups:
+- name: zfs
+  rules:
+    - alert: ZfsPoolDegraded
+      expr: node_zfs_zpool_state{state="degraded"} == 1
+      for: 5m
+      labels:
+        severity: warning
+      annotations:
+        summary: "ZFS pool {{ $labels.zpool }} is degraded on {{ $labels.instance }}"
+        description: "Pool {{ $labels.zpool }} on {{ $labels.instance }} has entered a degraded state. Check disk health immediately."
+
+    - alert: ZfsPoolFaulted
+      expr: node_zfs_zpool_state{state="faulted"} == 1
+      for: 1m
+      labels:
+        severity: critical
+      annotations:
+        summary: "ZFS pool {{ $labels.zpool }} is FAULTED on {{ $labels.instance }}"
+        description: "Pool {{ $labels.zpool }} on {{ $labels.instance }} is faulted. Data may be at risk."
+
+    - alert: ZfsPoolOffline
+      expr: node_zfs_zpool_state{state="offline"} == 1
+      for: 5m
+      labels:
+        severity: warning
+      annotations:
+        summary: "ZFS pool {{ $labels.zpool }} is offline on {{ $labels.instance }}"
+        description: "Pool {{ $labels.zpool }} on {{ $labels.instance }} is offline."