diff --git a/.github/workflows/test-ansible.yml b/.github/workflows/test-ansible.yml
index 61d81b0068..e8c523d95b 100644
--- a/.github/workflows/test-ansible.yml
+++ b/.github/workflows/test-ansible.yml
@@ -125,7 +125,7 @@ jobs:
           if [ -d "$role_path/molecule" ]; then
             echo "Testing role: $role_path"
             cd "$role_path"
-            molecule test
+            molecule test --all
           else
             echo "No molecule tests found for role: $role_path, skipping"
           fi
diff --git a/ansible/playbooks/control-plane.yml b/ansible/playbooks/control-plane.yml
index 5cec1a5a06..671ce06741 100644
--- a/ansible/playbooks/control-plane.yml
+++ b/ansible/playbooks/control-plane.yml
@@ -106,3 +106,4 @@
         kubelet_cluster_dns: "{{ cluster_dns }}"
         kubelet_cluster_domain: "{{ cluster_domain }}"
         kubelet_node_ip: "{{ node_ip }}"
+        journald_persistent_storage: true
diff --git a/ansible/roles/kubernetes_components/defaults/main.yml b/ansible/roles/kubernetes_components/defaults/main.yml
index 769581c102..befc3c1bd6 100644
--- a/ansible/roles/kubernetes_components/defaults/main.yml
+++ b/ansible/roles/kubernetes_components/defaults/main.yml
@@ -69,3 +69,12 @@ sysctl_config:
 # Increased from default 100m CPU / 100Mi memory to accommodate ARM processor characteristics
 etcd_resource_requests_cpu: "200m"
 etcd_resource_requests_memory: "200Mi"
+
+# journald persistent storage configuration
+# Disabled by default; enable explicitly for control-plane nodes where persistent logs are needed.
+# See playbooks/control-plane.yml for the enabling override.
+journald_persistent_storage: false
+# Set to true only when removing existing persistent journal history is intended.
+journald_purge_persistent_logs: false
+journald_system_max_use: "200M"
+journald_max_retention_sec: "1month"
diff --git a/ansible/roles/kubernetes_components/handlers/main.yml b/ansible/roles/kubernetes_components/handlers/main.yml
index b3d5abea27..c35efa214d 100644
--- a/ansible/roles/kubernetes_components/handlers/main.yml
+++ b/ansible/roles/kubernetes_components/handlers/main.yml
@@ -43,3 +43,13 @@
     - ansible_virtualization_type != "docker"
     - chroot_build is not defined or not chroot_build
   listen: "Restart kubelet"
+
+- name: Restart systemd-journald
+  ansible.builtin.systemd:
+    name: systemd-journald
+    state: restarted
+  become: true
+  when:
+    - ansible_virtualization_type != "docker"
+    - chroot_build is not defined or not chroot_build
+  listen: "Restart systemd-journald"
diff --git a/ansible/roles/kubernetes_components/molecule/default/converge.yml b/ansible/roles/kubernetes_components/molecule/default/converge.yml
index 02140d18c1..2fe0f8c4fe 100644
--- a/ansible/roles/kubernetes_components/molecule/default/converge.yml
+++ b/ansible/roles/kubernetes_components/molecule/default/converge.yml
@@ -7,4 +7,5 @@
   vars:
     # Test-specific overrides for container environment
     kubernetes_disable_swap: false  # Skip swap operations in container
-    kubernetes_enable_modules: false  # Skip module loading in container
\ No newline at end of file
+    kubernetes_enable_modules: false  # Skip module loading in container
+    journald_persistent_storage: true  # Validate the persistent-storage code path
\ No newline at end of file
diff --git a/ansible/roles/kubernetes_components/molecule/default/verify.yml b/ansible/roles/kubernetes_components/molecule/default/verify.yml
index cbbe614751..fafad04408 100644
--- a/ansible/roles/kubernetes_components/molecule/default/verify.yml
+++ b/ansible/roles/kubernetes_components/molecule/default/verify.yml
@@ -2,6 +2,8 @@
 - name: Verify
   hosts: all
   gather_facts: true
+  vars:
+    journald_persistent_storage: true
   tasks:
     - name: Check if CRI-O is installed
       ansible.builtin.package_facts:
@@ -144,3 +146,50 @@
         that:
           - "'1.32' in kubectl_version.stdout"
         fail_msg: "Kubectl version is not as expected"
+
+    - name: Check if persistent journal directory exists
+      ansible.builtin.stat:
+        path: /var/log/journal
+      register: journal_dir
+
+    - name: Assert persistent journal directory exists
+      ansible.builtin.assert:
+        that:
+          - journal_dir.stat.exists
+          - journal_dir.stat.isdir
+        fail_msg: "/var/log/journal directory does not exist — journald persistent storage not configured"
+      when: journald_persistent_storage | bool
+
+    - name: Check if journald drop-in config exists
+      ansible.builtin.stat:
+        path: /etc/systemd/journald.conf.d/10-persistent-storage.conf
+      register: journald_dropin
+
+    - name: Assert journald drop-in config is absent when persistent storage is disabled
+      ansible.builtin.assert:
+        that:
+          - not journald_dropin.stat.exists
+        fail_msg: "journald persistent-storage drop-in must be absent when persistent storage is disabled"
+      when: not (journald_persistent_storage | bool)
+
+    - name: Assert journald drop-in config exists when persistent storage is enabled
+      ansible.builtin.assert:
+        that:
+          - journald_dropin.stat.exists
+        fail_msg: "journald drop-in /etc/systemd/journald.conf.d/10-persistent-storage.conf does not exist"
+      when: journald_persistent_storage | bool
+
+    - name: Read journald drop-in config
+      ansible.builtin.slurp:
+        path: /etc/systemd/journald.conf.d/10-persistent-storage.conf
+      register: journald_dropin_content
+      when: journald_persistent_storage | bool
+
+    - name: Assert journald is configured for persistent storage
+      ansible.builtin.assert:
+        that:
+          - "'Storage=persistent' in (journald_dropin_content.content | b64decode)"
+          - "'SystemMaxUse=200M' in (journald_dropin_content.content | b64decode)"
+          - "'MaxRetentionSec=1month' in (journald_dropin_content.content | b64decode)"
+        fail_msg: "journald drop-in is missing Storage=persistent, SystemMaxUse=200M, or MaxRetentionSec=1month"
+      when: journald_persistent_storage | bool
diff --git a/ansible/roles/kubernetes_components/molecule/journald-disabled/converge.yml b/ansible/roles/kubernetes_components/molecule/journald-disabled/converge.yml
new file mode 100644
index 0000000000..1ae4d3f405
--- /dev/null
+++ b/ansible/roles/kubernetes_components/molecule/journald-disabled/converge.yml
@@ -0,0 +1,10 @@
+---
+- name: Converge
+  hosts: all
+  become: true
+  roles:
+    - role: ../../../../kubernetes_components
+  vars:
+    kubernetes_disable_swap: false
+    kubernetes_enable_modules: false
+    journald_persistent_storage: false  # Validate the disabled (volatile) code path
diff --git a/ansible/roles/kubernetes_components/molecule/journald-disabled/molecule.yml b/ansible/roles/kubernetes_components/molecule/journald-disabled/molecule.yml
new file mode 100644
index 0000000000..93b7b1020d
--- /dev/null
+++ b/ansible/roles/kubernetes_components/molecule/journald-disabled/molecule.yml
@@ -0,0 +1,29 @@
+---
+dependency:
+  name: galaxy
+driver:
+  name: docker
+platforms:
+  - name: instance
+    image: "geerlingguy/docker-ubuntu2404-ansible:latest"
+    platform: "${MOLECULE_DOCKER_PLATFORM:-linux/amd64}"
+    pre_build_image: true
+    privileged: true
+    volumes:
+      - /sys/fs/cgroup:/sys/fs/cgroup:rw
+    cgroupns_mode: host
+    command: /lib/systemd/systemd
+    env:
+      DEBIAN_FRONTEND: noninteractive
+    groups:
+      - orange_pi_zero3
+provisioner:
+  name: ansible
+  inventory:
+    host_vars:
+      instance:
+        ansible_python_interpreter: /usr/bin/python3
+        hardware_type: orange_pi_zero3
+        architecture: arm64
+verifier:
+  name: ansible
diff --git a/ansible/roles/kubernetes_components/molecule/journald-disabled/prepare.yml b/ansible/roles/kubernetes_components/molecule/journald-disabled/prepare.yml
new file mode 100644
index 0000000000..5cc6d744f5
--- /dev/null
+++ b/ansible/roles/kubernetes_components/molecule/journald-disabled/prepare.yml
@@ -0,0 +1,97 @@
+---
+- name: Prepare Orange Pi Zero 3 simulation environment
+  hosts: all
+  gather_facts: true
+  tasks:
+    - name: Update package cache
+      ansible.builtin.package:
+        update_cache: true
+      become: true
+
+    - name: Install required packages for Orange Pi Zero 3 simulation
+      ansible.builtin.package:
+        name:
+          - systemd
+          - dbus
+          - init
+          - iproute2
+          - kmod
+          - procps
+          - curl
+          - gnupg
+          - ca-certificates
+        state: present
+      become: true
+
+    - name: Create kernel modules directory
+      ansible.builtin.file:
+        path: /lib/modules
+        state: directory
+        mode: '0755'
+      become: true
+
+    - name: Ensure systemd is running
+      ansible.builtin.systemd:
+        name: systemd-logind
+        state: started
+      become: true
+      failed_when: false
+
+    - name: Create SSH host keys
+      ansible.builtin.command: ssh-keygen -A
+      become: true
+      changed_when: false
+      failed_when: false
+
+    - name: Create mock kernel modules for testing
+      ansible.builtin.shell: |
+        set -o pipefail
+        mkdir -p /lib/modules/$(uname -r)
+        touch /lib/modules/$(uname -r)/modules.dep
+        touch /lib/modules/$(uname -r)/modules.symbols
+      become: true
+      changed_when: false
+      failed_when: false
+
+    - name: Mock modprobe for container environment
+      ansible.builtin.copy:
+        dest: /usr/local/bin/modprobe
+        content: |
+          #!/bin/bash
+          # Mock modprobe for container testing
+          echo "Mock modprobe: $*"
+          exit 0
+        mode: '0755'
+      become: true
+
+    - name: Ensure journald drop-in directory exists
+      ansible.builtin.file:
+        path: /etc/systemd/journald.conf.d
+        state: directory
+        mode: '0755'
+      become: true
+
+    - name: Pre-create role-managed journald drop-in (simulates prior persistent-enable run)
+      ansible.builtin.copy:
+        dest: /etc/systemd/journald.conf.d/10-persistent-storage.conf
+        mode: '0644'
+        content: |
+          [Journal]
+          Storage=persistent
+          SystemMaxUse=200M
+          MaxRetentionSec=1month
+      become: true
+
+    - name: Pre-create /var/log/journal to simulate existing persistent journal
+      ansible.builtin.file:
+        path: /var/log/journal
+        state: directory
+        mode: '2755'
+      become: true
+
+    - name: Create a sentinel file inside /var/log/journal to confirm non-destructive behavior
+      ansible.builtin.copy:
+        dest: /var/log/journal/.keep
+        content: "pre-existing log marker"
+        mode: '0644'
+      become: true
diff --git a/ansible/roles/kubernetes_components/molecule/journald-disabled/verify.yml b/ansible/roles/kubernetes_components/molecule/journald-disabled/verify.yml
new file mode 100644
index 0000000000..3f5782c9ed
--- /dev/null
+++ b/ansible/roles/kubernetes_components/molecule/journald-disabled/verify.yml
@@ -0,0 +1,44 @@
+---
+- name: Verify journald disabled path
+  hosts: all
+  gather_facts: false
+  tasks:
+    - name: Stat journald drop-in file
+      ansible.builtin.stat:
+        path: /etc/systemd/journald.conf.d/10-persistent-storage.conf
+      register: journald_dropin_stat
+
+    - name: Assert drop-in is absent when persistent storage is disabled
+      ansible.builtin.assert:
+        that:
+          - not journald_dropin_stat.stat.exists
+        fail_msg: >-
+          journald drop-in must be absent when journald_persistent_storage is false,
+          but the file exists at /etc/systemd/journald.conf.d/10-persistent-storage.conf
+
+    - name: Stat /var/log/journal directory
+      ansible.builtin.stat:
+        path: /var/log/journal
+      register: journal_dir_stat
+
+    - name: Assert /var/log/journal is preserved (non-destructive when disabled)
+      ansible.builtin.assert:
+        that:
+          - journal_dir_stat.stat.exists
+          - journal_dir_stat.stat.isdir
+        fail_msg: >-
+          /var/log/journal must be preserved when journald_persistent_storage is false —
+          the role must not destroy existing log data
+
+    - name: Stat sentinel file inside /var/log/journal
+      ansible.builtin.stat:
+        path: /var/log/journal/.keep
+      register: journal_keep_stat
+
+    - name: Assert sentinel file is preserved (pre-existing logs not deleted)
+      ansible.builtin.assert:
+        that:
+          - journal_keep_stat.stat.exists
+        fail_msg: >-
+          Pre-existing /var/log/journal/.keep was deleted — the role must not purge existing logs
+          unless journald_purge_persistent_logs is explicitly set to true
diff --git a/ansible/roles/kubernetes_components/molecule/journald-purge/converge.yml b/ansible/roles/kubernetes_components/molecule/journald-purge/converge.yml
new file mode 100644
index 0000000000..39e1652099
--- /dev/null
+++ b/ansible/roles/kubernetes_components/molecule/journald-purge/converge.yml
@@ -0,0 +1,11 @@
+---
+- name: Converge
+  hosts: all
+  become: true
+  roles:
+    - role: ../../../../kubernetes_components
+  vars:
+    kubernetes_disable_swap: false
+    kubernetes_enable_modules: false
+    journald_persistent_storage: false
+    journald_purge_persistent_logs: true  # Validate the explicit purge opt-in path
diff --git a/ansible/roles/kubernetes_components/molecule/journald-purge/molecule.yml b/ansible/roles/kubernetes_components/molecule/journald-purge/molecule.yml
new file mode 100644
index 0000000000..93b7b1020d
--- /dev/null
+++ b/ansible/roles/kubernetes_components/molecule/journald-purge/molecule.yml
@@ -0,0 +1,29 @@
+---
+dependency:
+  name: galaxy
+driver:
+  name: docker
+platforms:
+  - name: instance
+    image: "geerlingguy/docker-ubuntu2404-ansible:latest"
+    platform: "${MOLECULE_DOCKER_PLATFORM:-linux/amd64}"
+    pre_build_image: true
+    privileged: true
+    volumes:
+      - /sys/fs/cgroup:/sys/fs/cgroup:rw
+    cgroupns_mode: host
+    command: /lib/systemd/systemd
+    env:
+      DEBIAN_FRONTEND: noninteractive
+    groups:
+      - orange_pi_zero3
+provisioner:
+  name: ansible
+  inventory:
+    host_vars:
+      instance:
+        ansible_python_interpreter: /usr/bin/python3
+        hardware_type: orange_pi_zero3
+        architecture: arm64
+verifier:
+  name: ansible
diff --git a/ansible/roles/kubernetes_components/molecule/journald-purge/prepare.yml b/ansible/roles/kubernetes_components/molecule/journald-purge/prepare.yml
new file mode 100644
index 0000000000..8d19222f50
--- /dev/null
+++ b/ansible/roles/kubernetes_components/molecule/journald-purge/prepare.yml
@@ -0,0 +1,97 @@
+---
+- name: Prepare environment for journald purge scenario
+  hosts: all
+  gather_facts: true
+  tasks:
+    - name: Update package cache
+      ansible.builtin.package:
+        update_cache: true
+      become: true
+
+    - name: Install required packages
+      ansible.builtin.package:
+        name:
+          - systemd
+          - dbus
+          - init
+          - iproute2
+          - kmod
+          - procps
+          - curl
+          - gnupg
+          - ca-certificates
+        state: present
+      become: true
+
+    - name: Create kernel modules directory
+      ansible.builtin.file:
+        path: /lib/modules
+        state: directory
+        mode: '0755'
+      become: true
+
+    - name: Ensure systemd is running
+      ansible.builtin.systemd:
+        name: systemd-logind
+        state: started
+      become: true
+      failed_when: false
+
+    - name: Create SSH host keys
+      ansible.builtin.command: ssh-keygen -A
+      become: true
+      changed_when: false
+      failed_when: false
+
+    - name: Create mock kernel modules for testing
+      ansible.builtin.shell: |
+        set -o pipefail
+        mkdir -p /lib/modules/$(uname -r)
+        touch /lib/modules/$(uname -r)/modules.dep
+        touch /lib/modules/$(uname -r)/modules.symbols
+      become: true
+      changed_when: false
+      failed_when: false
+
+    - name: Mock modprobe for container environment
+      ansible.builtin.copy:
+        dest: /usr/local/bin/modprobe
+        content: |
+          #!/bin/bash
+          # Mock modprobe for container testing
+          echo "Mock modprobe: $*"
+          exit 0
+        mode: '0755'
+      become: true
+
+    - name: Ensure journald drop-in directory exists
+      ansible.builtin.file:
+        path: /etc/systemd/journald.conf.d
+        state: directory
+        mode: '0755'
+      become: true
+
+    - name: Pre-create role-managed journald drop-in (simulates prior persistent-enable run)
+      ansible.builtin.copy:
+        dest: /etc/systemd/journald.conf.d/10-persistent-storage.conf
+        mode: '0644'
+        content: |
+          [Journal]
+          Storage=persistent
+          SystemMaxUse=200M
+          MaxRetentionSec=1month
+      become: true
+
+    - name: Pre-create /var/log/journal directory (simulates existing persistent journal)
+      ansible.builtin.file:
+        path: /var/log/journal
+        state: directory
+        mode: '2755'
+      become: true
+
+    - name: Pre-create sentinel file inside /var/log/journal
+      ansible.builtin.copy:
+        dest: /var/log/journal/existing-log.journal
+        content: "sentinel"
+        mode: '0644'
+      become: true
diff --git a/ansible/roles/kubernetes_components/molecule/journald-purge/verify.yml b/ansible/roles/kubernetes_components/molecule/journald-purge/verify.yml
new file mode 100644
index 0000000000..897ee69dbe
--- /dev/null
+++ b/ansible/roles/kubernetes_components/molecule/journald-purge/verify.yml
@@ -0,0 +1,43 @@
+---
+- name: Verify journald purge path
+  hosts: all
+  gather_facts: false
+  tasks:
+    - name: Check if role-managed journald drop-in was removed
+      ansible.builtin.stat:
+        path: /etc/systemd/journald.conf.d/10-persistent-storage.conf
+      register: journald_dropin
+
+    - name: Assert role-managed drop-in is absent
+      ansible.builtin.assert:
+        that:
+          - not journald_dropin.stat.exists
+        fail_msg: >-
+          /etc/systemd/journald.conf.d/10-persistent-storage.conf must be absent
+          when journald_persistent_storage is false.
+
+    - name: Check if /var/log/journal was purged
+      ansible.builtin.stat:
+        path: /var/log/journal
+      register: journal_dir
+
+    - name: Assert /var/log/journal was deleted when purge flag is set
+      ansible.builtin.assert:
+        that:
+          - not journal_dir.stat.exists
+        fail_msg: >-
+          /var/log/journal must be deleted when journald_purge_persistent_logs is true,
+          but the directory still exists.
+
+    - name: Check if sentinel file was purged
+      ansible.builtin.stat:
+        path: /var/log/journal/existing-log.journal
+      register: sentinel_file
+
+    - name: Assert sentinel file inside /var/log/journal was also deleted
+      ansible.builtin.assert:
+        that:
+          - not sentinel_file.stat.exists
+        fail_msg: >-
+          Sentinel file /var/log/journal/existing-log.journal must be deleted
+          when journald_purge_persistent_logs is true.
diff --git a/ansible/roles/kubernetes_components/tasks/journald.yml b/ansible/roles/kubernetes_components/tasks/journald.yml
new file mode 100644
index 0000000000..68d44f9155
--- /dev/null
+++ b/ansible/roles/kubernetes_components/tasks/journald.yml
@@ -0,0 +1,49 @@
+---
+# Persist host logs so pre-reboot storage/kernel errors survive when media is still readable.
+# Bounded by journald_system_max_use to avoid exhausting the SD card on control-plane nodes.
+# Only enabled when journald_persistent_storage: true (set per-playbook, not globally).
+
+- name: Ensure persistent journald directory exists
+  ansible.builtin.file:
+    path: /var/log/journal
+    state: directory
+    mode: '2755'
+  become: true
+  when: journald_persistent_storage | bool
+  notify: Restart systemd-journald
+
+- name: Ensure journald drop-in directory exists
+  ansible.builtin.file:
+    path: /etc/systemd/journald.conf.d
+    state: directory
+    mode: '0755'
+  become: true
+
+- name: Configure bounded persistent journald storage
+  ansible.builtin.copy:
+    dest: /etc/systemd/journald.conf.d/10-persistent-storage.conf
+    mode: '0644'
+    content: |
+      [Journal]
+      Storage=persistent
+      SystemMaxUse={{ journald_system_max_use }}
+      MaxRetentionSec={{ journald_max_retention_sec }}
+  become: true
+  when: journald_persistent_storage | bool
+  notify: Restart systemd-journald
+
+- name: Remove role-managed journald drop-in when persistent storage is disabled
+  ansible.builtin.file:
+    path: /etc/systemd/journald.conf.d/10-persistent-storage.conf
+    state: absent
+  become: true
+  when: not (journald_persistent_storage | bool)
+  notify: Restart systemd-journald
+
+- name: Purge persistent journal directory (explicit opt-in only)
+  ansible.builtin.file:
+    path: /var/log/journal
+    state: absent
+  become: true
+  when: not (journald_persistent_storage | bool) and (journald_purge_persistent_logs | bool)
+  notify: Restart systemd-journald
diff --git a/ansible/roles/kubernetes_components/tasks/main.yml b/ansible/roles/kubernetes_components/tasks/main.yml
index d573e3bf47..7f02eece3e 100644
--- a/ansible/roles/kubernetes_components/tasks/main.yml
+++ b/ansible/roles/kubernetes_components/tasks/main.yml
@@ -15,3 +15,6 @@
 
 - name: Include kubeadm configuration tasks
   ansible.builtin.include_tasks: kubeadm.yml
+
+- name: Include journald configuration tasks
+  ansible.builtin.include_tasks: journald.yml
diff --git a/docs/project_docs/BOXP-127/plan.md b/docs/project_docs/BOXP-127/plan.md
new file mode 100644
index 0000000000..b0dc64ce23
--- /dev/null
+++ b/docs/project_docs/BOXP-127/plan.md
@@ -0,0 +1,65 @@
+# BOXP-127: control-plane ノード電源断原因調査と恒久対策
+
+## 根本原因
+
+Orange Pi Zero3 の control-plane ノード（shanghai-1/2/3）が繰り返し到達不能になる原因は、**microSD カードの書き込み耐久性不足**による OS フリーズ・ファイルシステム read-only 化。
+
+- INC-2（2026-07-06, shanghai-2）: SD カード障害 → OS 再イメージで復旧
+- INC-4（2026-07-12, shanghai-2）: 交換後わずか 7 日で再障害 → etcd WAL 書き込み負荷による急速摩耗
+- BOXP-127（2026-07-22, shanghai-1）: 同パターン
+
+## 即座の対応（実施済み・手動）
+
+1. shanghai-1 の電源サイクル（ユーザーが 2026-07-23 に実施）
+2. 起動しない場合は `shanghai-control-plane-sdcard-failure.md` runbook に従い SD カード交換 → etcd member re-join
+
+## 恒久対策の優先順位
+
+### 1. journald 永続化（本 PR: arch repo）
+
+`kubernetes_components` Ansible ロールに journald.yml タスクを追加。
+
+- `/var/log/journal` ディレクトリを作成し `Storage=persistent` に設定
+- `SystemMaxUse=200M`, `MaxRetentionSec=1month` で SD カード消費を抑制
+- デフォルト無効（`journald_persistent_storage: false`）。control-plane playbook 側で `true` に設定することで control-plane ノード限定で有効化。worker ノードには適用されない
+- 次回 Ansible Apply 時に全 control-plane ノードに適用される
+
+**効果**: 次回 SD カード障害時に障害直前のカーネルログ・ストレージエラー（`EXT4-fs error`, `mmcblk0: error -110`）が保存され、根本原因の確定が可能になる。
+
+### 2. Alertmanager ルール追加（lolice repo: feature/control-plane-node-alert ブランチ）
+
+`control-plane-node-rules.yaml` に以下のアラートを追加:
+
+| アラート名 | 条件 | 重要度 |
+|---|---|---|
+| `ControlPlaneNodeNotReady` | control-plane ノードが 5 分以上 NotReady | critical |
+| `EtcdMemberDown` | etcd member 数が 2 未満 | critical |
+| `EtcdHighFsyncDuration` | WAL fsync p99 > 500ms が 10 分継続 | warning |
+| `ControlPlaneFilesystemReadOnly` | `/`, `/var`, `/var/lib` が read-only | critical |
+| `ControlPlaneHighDiskIOWait` | mmcblk デバイスの I/O 使用率 > 90% が 15 分継続 | warning |
+
+### 3. 高耐久メディアへの移行（今後の実施）
+
+優先順位:
+1. **高耐久 microSD（A2/SLC キャッシュ付き）への交換**: Samsung PRO Endurance / Western Digital Purple SC QD101 / SanDisk MAX Endurance などを推奨。TBW 値が通常品の 10〜40 倍。
+2. **USB SSD への移行（最優先推奨）**: etcd データディレクトリ（`/var/lib/etcd`）を USB SSD にバインドマウント。SD カードを読み取り専用 OS 起動用に限定。
+3. **eMMC への移行**: Orange Pi Zero3 には eMMC スロットがない（ボード非対応）ため対象外。
+
+## 実施済み変更
+
+- `arch/ansible/roles/kubernetes_components/tasks/journald.yml`: journald 永続化タスク（新規）
+- `arch/ansible/roles/kubernetes_components/tasks/main.yml`: journald.yml を include
+- `arch/ansible/roles/kubernetes_components/defaults/main.yml`: `journald_persistent_storage` デフォルト変数追加
+- `arch/ansible/roles/kubernetes_components/handlers/main.yml`: `Restart systemd-journald` ハンドラ追加
+- `lolice/argoproj/prometheus-operator/control-plane-node-rules.yaml`: etcd・SDカード I/O アラート追加
+
+## journald 無効時の設計方針
+
+`journald_persistent_storage: false`（ロールデフォルト）では:
+
+1. **ロール管理の drop-in のみを削除する**（`state: absent`）。`Storage=volatile` を書き込むことはしない。
+2. **既存の `/var/log/journal` は保持する**。ログの破壊的削除は `journald_purge_persistent_logs: true` の明示指定時だけ行う。
+3. **Storage=auto 動作への委任は意図的な設計**。drop-in 不在で journald はデフォルトの `Storage=auto` に戻る。新規ノードや `/var/log/journal` を持たないノードでは volatile になり永続化しない。これが worker ノードの想定動作。
+4. **Molecule 検証**では、無効時に drop-in が存在しないことを確認する（`journald-disabled` シナリオ）。
+
+> `/var/log/journal` が既に存在するホストで false に切り替えた場合、`Storage=auto` により journald が引き続き永続化する可能性がある。これは既存ログを保全するための意図的な非破壊設計。そのようなホストで完全に volatile に戻したい場合は `journald_purge_persistent_logs: true` を使用すること。