docs(monitoring): stop treating a worn EPHEMERAL drive as a hazard

I described the worn drives carrying EPHEMERAL as the dangerous placement,
repeatedly, in the alert text and in the dashboard's caveats. That reads the
volume backwards. EPHEMERAL is Talos's /var and its contents are meant to be
disposable — container images, kubelet state, pod scratch, spegel and Rook's
local state all rebuild. Putting the drives with the least endurance left there
is a sensible destination, not a risk someone should be warned about.

The alert said "a node simply stops when it goes", which is simply wrong. A node
losing /var rebuilds it.

What survives the correction is narrower and checked rather than recalled:
/var/lib/etcd is on that volume too, so losing EPHEMERAL on a control-plane node
costs that member's data. Quorum holds at two of three and the member is removed
and re-added. That is a rebuild, not data loss, and the alert now says so at
that weight.

The fill-level panel keeps its warning but for the right reason: a full /var
stops a node being useful long before anything is lost, and nothing rebalances
it the way Ceph rebalances a full OSD. That is a capacity argument, not an
endurance one.

None of this changes the monitoring — measuring every drive is still right, and
the wear figures are unchanged. It changes what a reader is told the numbers
mean, which is the part that was misleading.

Refs #549

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

kubernetes/apps/monitoring-rules/prometheusrule-disk-wear.yaml

@@ -38,11 +38,15 @@ spec:
             summary: "NVMe {{ $labels.device }} on {{ $labels.instance }} is at {{ $value }}% rated wear"
             description: >-
               The drive has used {{ $value }}% of its rated write endurance.
-              Nothing is failing and no data is at risk yet. Check what the
-              drive is carrying before deciding urgency: an OSD is replaceable
-              with a rebalance, whereas the EPHEMERAL volume has no such
-              escape — a node simply stops when it goes. The Disk Health
-              dashboard resolves which drive holds which role.
+              Nothing is failing and no data is at risk yet. What the drive
+              carries decides the urgency, and the Disk Health dashboard
+              resolves which role it holds. An OSD losing a drive costs a
+              rebalance. EPHEMERAL is Talos's /var and is meant to be
+              disposable — container images, kubelet state and pod scratch all
+              rebuild — so a worn drive there is a reasonable place for it. The
+              one thing on that volume which is not free to lose is the node's
+              etcd member data: quorum survives losing one of three, but the
+              member has to be removed and re-added.
         - alert: NvmeDriveWearCritical
           expr: smartctl_device_percentage_used >= 95
           for: 1h

kubernetes/apps/monitoring/dashboards/disk-health.json

@@ -1,6 +1,6 @@
 {
   "annotations": {"list": []},
-  "description": "NVMe health and performance per node. The top row answers 'is anything wrong'; the graphs below answer 'why'. Panels resolve each drive through node_nvme_info and node_uname_info rather than plotting the Linux device name, because NVMe enumeration order is not guaranteed to agree across machines — the same name can be a different drive on the next node. Which drive currently holds which role is in the inventory table, deliberately not in this text. Endurance/wear is absent; see the note at the bottom and issue #549.",
+  "description": "NVMe health and performance per node. The top row answers 'is anything wrong'; the graphs below answer 'why'. Panels resolve each drive through node_nvme_info and node_uname_info rather than plotting the Linux device name, because NVMe enumeration order is not guaranteed to agree across machines — the same name can be a different drive on the next node. Which drive currently holds which role is in the inventory table, deliberately not in this text. Endurance comes from smartctl_exporter, whose series are labelled by node rather than by the exporter pod's IP — see the note at the bottom for what it still cannot tell you.",
   "editable": true,
   "fiscalYearStartMonth": 0,
   "graphTooltip": 1,
@@ -19,7 +19,7 @@
         },
         "overrides": []
       },
-      "gridPos": {"h": 4, "w": 6, "x": 0, "y": 0},
+      "gridPos": {"h": 4, "w": 5, "x": 0, "y": 0},
       "id": 10,
       "options": {"colorMode": "background", "graphMode": "none", "justifyMode": "auto", "orientation": "auto", "reduceOptions": {"calcs": ["lastNotNull"], "fields": "", "values": false}, "textMode": "auto"},
       "targets": [{"datasource": {"type": "prometheus", "uid": "prometheus"}, "expr": "ceph_health_status", "legendFormat": "", "refId": "A"}],
@@ -28,7 +28,7 @@
     },
     {
       "datasource": {"type": "prometheus", "uid": "prometheus"},
-      "description": "OSDs the cluster knows about but which are not up, and not in. Both should read zero. Counted as a difference against ceph_osd_metadata rather than compared to a fixed number, so adding or removing an OSD does not turn this panel into a false alarm.",
+      "description": "OSDs the cluster knows about but which are not up. Should read zero. Counted as a difference against ceph_osd_metadata rather than compared to a fixed number, so adding or removing an OSD does not turn this panel into a false alarm. An OSD that is up but out shows as a Ceph health warning instead — it is a state, not a fault, and it does not belong in a red-or-green box.",
       "fieldConfig": {
         "defaults": {
           "color": {"mode": "thresholds"},
@@ -38,14 +38,13 @@
         },
         "overrides": []
       },
-      "gridPos": {"h": 4, "w": 6, "x": 6, "y": 0},
+      "gridPos": {"h": 4, "w": 5, "x": 5, "y": 0},
       "id": 11,
       "options": {"colorMode": "background", "graphMode": "none", "justifyMode": "auto", "orientation": "auto", "reduceOptions": {"calcs": ["lastNotNull"], "fields": "", "values": false}, "textMode": "auto"},
       "targets": [
-        {"datasource": {"type": "prometheus", "uid": "prometheus"}, "expr": "sum(ceph_osd_metadata) - sum(ceph_osd_up)", "legendFormat": "down", "refId": "A"},
-        {"datasource": {"type": "prometheus", "uid": "prometheus"}, "expr": "sum(ceph_osd_metadata) - sum(ceph_osd_in)", "legendFormat": "out", "refId": "B"}
+        {"datasource": {"type": "prometheus", "uid": "prometheus"}, "expr": "sum(ceph_osd_metadata) - sum(ceph_osd_up)", "legendFormat": "", "refId": "A"}
       ],
-      "title": "OSDs down / out",
+      "title": "OSDs down",
       "type": "stat"
     },
     {
@@ -62,7 +61,7 @@
         },
         "overrides": []
       },
-      "gridPos": {"h": 4, "w": 6, "x": 12, "y": 0},
+      "gridPos": {"h": 4, "w": 5, "x": 10, "y": 0},
       "id": 12,
       "options": {"colorMode": "background", "graphMode": "area", "justifyMode": "auto", "orientation": "auto", "reduceOptions": {"calcs": ["lastNotNull"], "fields": "", "values": false}, "textMode": "auto"},
       "targets": [{"datasource": {"type": "prometheus", "uid": "prometheus"}, "expr": "ceph_cluster_total_used_bytes / ceph_cluster_total_bytes", "legendFormat": "", "refId": "A"}],
@@ -71,7 +70,7 @@
     },
     {
       "datasource": {"type": "prometheus", "uid": "prometheus"},
-      "description": "Fullest EPHEMERAL volume across the fleet — Talos's /var, holding container images, pod scratch space and kubelet state. A full /var takes the node down, and unlike Ceph nothing rebalances away from it.",
+      "description": "Fullest EPHEMERAL volume across the fleet — Talos's /var. Its contents are meant to be disposable: container images, kubelet state and pod scratch all rebuild. Filling it is still a problem, because a node with no room to write stops being useful long before anything is lost, and nothing rebalances /var the way Ceph rebalances a full OSD.",
       "fieldConfig": {
         "defaults": {
           "color": {"mode": "thresholds"},
@@ -83,7 +82,7 @@
         },
         "overrides": []
       },
-      "gridPos": {"h": 4, "w": 6, "x": 18, "y": 0},
+      "gridPos": {"h": 4, "w": 5, "x": 15, "y": 0},
       "id": 13,
       "options": {"colorMode": "background", "graphMode": "area", "justifyMode": "auto", "orientation": "auto", "reduceOptions": {"calcs": ["lastNotNull"], "fields": "", "values": false}, "textMode": "auto"},
       "targets": [{"datasource": {"type": "prometheus", "uid": "prometheus"}, "expr": "max(1 - node_filesystem_avail_bytes{mountpoint=\"/var\"} / node_filesystem_size_bytes{mountpoint=\"/var\"})", "legendFormat": "", "refId": "A"}],
@@ -115,7 +114,7 @@
           "refId": "A"
         }
       ],
-      "title": "Drive inventory",
+      "title": "Drive inventory (identity and role)",
       "transformations": [
         {
           "id": "organize",
@@ -128,6 +127,100 @@
       ],
       "type": "table"
     },
+    {
+      "datasource": {"type": "prometheus", "uid": "prometheus"},
+      "description": "Rated endurance consumed, worst drive in the fleet. This is the drive's own accounting against what the manufacturer warrants, not a failure prediction — a drive past 100 usually keeps working and starts eating its spare area. Read it for planning; read the SMART table for whether anything is failing now.",
+      "fieldConfig": {
+        "defaults": {
+          "color": {"mode": "thresholds"},
+          "mappings": [],
+          "max": 100,
+          "min": 0,
+          "thresholds": {"mode": "absolute", "steps": [{"color": "green", "value": null}, {"color": "orange", "value": 80}, {"color": "red", "value": 95}]},
+          "unit": "percent"
+        },
+        "overrides": []
+      },
+      "gridPos": {"h": 4, "w": 4, "x": 20, "y": 0},
+      "id": 14,
+      "options": {"colorMode": "background", "graphMode": "area", "justifyMode": "auto", "orientation": "auto", "reduceOptions": {"calcs": ["lastNotNull"], "fields": "", "values": false}, "textMode": "auto"},
+      "targets": [{"datasource": {"type": "prometheus", "uid": "prometheus"}, "expr": "max(smartctl_device_percentage_used)", "legendFormat": "", "refId": "A"}],
+      "title": "Worst NVMe wear",
+      "type": "stat"
+    },
+    {
+      "datasource": {"type": "prometheus", "uid": "prometheus"},
+      "description": "Rated endurance consumed per drive. The line is nearly flat by nature — wear moves on a scale of weeks — so the useful reading is the spread between drives and the slope, not today's value. Joined to smartctl_device for the model name, because the device label alone is not comparable across nodes.",
+      "fieldConfig": {
+        "defaults": {
+          "color": {"mode": "palette-classic"},
+          "custom": {"axisCenteredZero": false, "axisColorMode": "text", "axisPlacement": "auto", "barAlignment": 0, "drawStyle": "line", "fillOpacity": 10, "gradientMode": "none", "hideFrom": {"legend": false, "tooltip": false, "viz": false}, "lineInterpolation": "smooth", "lineWidth": 2, "pointSize": 5, "scaleDistribution": {"type": "linear"}, "showPoints": "never", "spanNulls": false, "stacking": {"group": "A", "mode": "none"}, "thresholdsStyle": {"mode": "dashed"}},
+          "mappings": [],
+          "max": 100,
+          "min": 0,
+          "thresholds": {"mode": "absolute", "steps": [{"color": "green", "value": null}, {"color": "orange", "value": 80}, {"color": "red", "value": 95}]},
+          "unit": "percent"
+        },
+        "overrides": []
+      },
+      "gridPos": {"h": 9, "w": 12, "x": 0, "y": 13},
+      "id": 15,
+      "options": {"legend": {"calcs": ["last"], "displayMode": "table", "placement": "bottom", "showLegend": true}, "tooltip": {"mode": "multi", "sort": "desc"}},
+      "targets": [
+        {
+          "datasource": {"type": "prometheus", "uid": "prometheus"},
+          "expr": "smartctl_device_percentage_used * on (node, device) group_left(model_name) smartctl_device",
+          "legendFormat": "{{node}} {{model_name}}",
+          "refId": "A"
+        }
+      ],
+      "title": "NVMe wear",
+      "type": "timeseries"
+    },
+    {
+      "datasource": {"type": "prometheus", "uid": "prometheus"},
+      "description": "The failure-now signals, as opposed to the endurance budget above. Spare below its threshold means the drive has run out of blocks to remap defects into; media errors are unrecoverable data-integrity failures and should never increment; the critical warning is a bitfield the drive raises itself. Written bytes is the counter behind the wear percentage, useful for projecting when a drive will reach it.",
+      "fieldConfig": {
+        "defaults": {
+          "color": {"mode": "thresholds"},
+          "custom": {"align": "auto", "cellOptions": {"type": "auto"}, "inspect": false},
+          "mappings": [],
+          "thresholds": {"mode": "absolute", "steps": [{"color": "text", "value": null}]}
+        },
+        "overrides": [
+          {"matcher": {"id": "byName", "options": "wear"}, "properties": [{"id": "unit", "value": "percent"}, {"id": "custom.cellOptions", "value": {"type": "color-text"}}, {"id": "thresholds", "value": {"mode": "absolute", "steps": [{"color": "green", "value": null}, {"color": "orange", "value": 80}, {"color": "red", "value": 95}]}}]},
+          {"matcher": {"id": "byName", "options": "spare"}, "properties": [{"id": "unit", "value": "percent"}]},
+          {"matcher": {"id": "byName", "options": "media errors"}, "properties": [{"id": "custom.cellOptions", "value": {"type": "color-text"}}, {"id": "thresholds", "value": {"mode": "absolute", "steps": [{"color": "green", "value": null}, {"color": "red", "value": 1}]}}]},
+          {"matcher": {"id": "byName", "options": "critical warning"}, "properties": [{"id": "custom.cellOptions", "value": {"type": "color-text"}}, {"id": "thresholds", "value": {"mode": "absolute", "steps": [{"color": "green", "value": null}, {"color": "red", "value": 1}]}}]},
+          {"matcher": {"id": "byName", "options": "powered on"}, "properties": [{"id": "unit", "value": "s"}]},
+          {"matcher": {"id": "byName", "options": "written"}, "properties": [{"id": "unit", "value": "bytes"}]}
+        ]
+      },
+      "gridPos": {"h": 9, "w": 12, "x": 12, "y": 13},
+      "id": 16,
+      "options": {"cellHeight": "sm", "footer": {"countRows": false, "fields": "", "reducer": ["sum"], "show": false}, "showHeader": true, "sortBy": [{"desc": true, "displayName": "wear"}]},
+      "targets": [
+        {"datasource": {"type": "prometheus", "uid": "prometheus"}, "expr": "smartctl_device_percentage_used * on (node, device) group_left(model_name) smartctl_device", "format": "table", "instant": true, "refId": "A"},
+        {"datasource": {"type": "prometheus", "uid": "prometheus"}, "expr": "smartctl_device_available_spare * on (node, device) group_left(model_name) smartctl_device", "format": "table", "instant": true, "refId": "B"},
+        {"datasource": {"type": "prometheus", "uid": "prometheus"}, "expr": "smartctl_device_media_errors * on (node, device) group_left(model_name) smartctl_device", "format": "table", "instant": true, "refId": "C"},
+        {"datasource": {"type": "prometheus", "uid": "prometheus"}, "expr": "smartctl_device_critical_warning * on (node, device) group_left(model_name) smartctl_device", "format": "table", "instant": true, "refId": "D"},
+        {"datasource": {"type": "prometheus", "uid": "prometheus"}, "expr": "smartctl_device_power_on_seconds * on (node, device) group_left(model_name) smartctl_device", "format": "table", "instant": true, "refId": "E"},
+        {"datasource": {"type": "prometheus", "uid": "prometheus"}, "expr": "smartctl_device_bytes_written * on (node, device) group_left(model_name) smartctl_device", "format": "table", "instant": true, "refId": "F"}
+      ],
+      "title": "SMART health",
+      "transformations": [
+        {"id": "merge", "options": {}},
+        {
+          "id": "organize",
+          "options": {
+            "excludeByName": {"Time": true, "__name__": true, "container": true, "endpoint": true, "instance": true, "job": true, "namespace": true, "pod": true, "service": true},
+            "indexByName": {},
+            "renameByName": {"node": "node", "device": "device", "model_name": "model", "Value #A": "wear", "Value #B": "spare", "Value #C": "media errors", "Value #D": "critical warning", "Value #E": "powered on", "Value #F": "written"}
+          }
+        }
+      ],
+      "type": "table"
+    },
     {
       "datasource": {"type": "prometheus", "uid": "prometheus"},
       "description": "Read and write throughput per drive.",
@@ -141,7 +234,7 @@
         },
         "overrides": []
       },
-      "gridPos": {"h": 9, "w": 12, "x": 0, "y": 13},
+      "gridPos": {"h": 9, "w": 12, "x": 0, "y": 22},
       "id": 2,
       "options": {"legend": {"calcs": ["mean", "max"], "displayMode": "table", "placement": "bottom", "showLegend": true}, "tooltip": {"mode": "multi", "sort": "desc"}},
       "targets": [
@@ -174,7 +267,7 @@
         },
         "overrides": []
       },
-      "gridPos": {"h": 9, "w": 12, "x": 12, "y": 13},
+      "gridPos": {"h": 9, "w": 12, "x": 12, "y": 22},
       "id": 3,
       "options": {"legend": {"calcs": ["mean", "max"], "displayMode": "table", "placement": "bottom", "showLegend": true}, "tooltip": {"mode": "multi", "sort": "desc"}},
       "targets": [
@@ -207,7 +300,7 @@
         },
         "overrides": []
       },
-      "gridPos": {"h": 9, "w": 12, "x": 0, "y": 22},
+      "gridPos": {"h": 9, "w": 12, "x": 0, "y": 31},
       "id": 4,
       "options": {"legend": {"calcs": ["mean", "max"], "displayMode": "table", "placement": "bottom", "showLegend": true}, "tooltip": {"mode": "multi", "sort": "desc"}},
       "targets": [
@@ -245,7 +338,7 @@
           }
         ]
       },
-      "gridPos": {"h": 9, "w": 12, "x": 12, "y": 22},
+      "gridPos": {"h": 9, "w": 12, "x": 12, "y": 31},
       "id": 5,
       "options": {"legend": {"calcs": ["mean", "max"], "displayMode": "table", "placement": "bottom", "showLegend": true}, "tooltip": {"mode": "multi", "sort": "desc"}},
       "targets": [
@@ -278,7 +371,7 @@
         },
         "overrides": []
       },
-      "gridPos": {"h": 9, "w": 12, "x": 0, "y": 31},
+      "gridPos": {"h": 9, "w": 12, "x": 0, "y": 40},
       "id": 6,
       "options": {"legend": {"calcs": ["mean", "max"], "displayMode": "table", "placement": "bottom", "showLegend": true}, "tooltip": {"mode": "multi", "sort": "desc"}},
       "targets": [
@@ -305,7 +398,7 @@
         },
         "overrides": []
       },
-      "gridPos": {"h": 9, "w": 12, "x": 12, "y": 31},
+      "gridPos": {"h": 9, "w": 12, "x": 12, "y": 40},
       "id": 7,
       "options": {"legend": {"calcs": ["mean", "max"], "displayMode": "table", "placement": "bottom", "showLegend": true}, "tooltip": {"mode": "multi", "sort": "desc"}},
       "targets": [
@@ -340,7 +433,7 @@
         },
         "overrides": []
       },
-      "gridPos": {"h": 8, "w": 24, "x": 0, "y": 40},
+      "gridPos": {"h": 8, "w": 24, "x": 0, "y": 49},
       "id": 9,
       "options": {"legend": {"calcs": ["last", "max"], "displayMode": "table", "placement": "bottom", "showLegend": true}, "tooltip": {"mode": "multi", "sort": "desc"}},
       "targets": [
@@ -356,11 +449,11 @@
     },
     {
       "datasource": {"type": "prometheus", "uid": "prometheus"},
-      "gridPos": {"h": 11, "w": 24, "x": 0, "y": 48},
+      "gridPos": {"h": 11, "w": 24, "x": 0, "y": 57},
       "id": 8,
       "options": {
         "code": {"language": "plaintext", "showLineNumbers": false, "showMiniMap": false},
-        "content": "### What this dashboard cannot tell you\n\nThese notes are about mechanisms, not about the drives currently fitted. The inventory table above is the live answer to what is in the machines; nothing here restates it, because prose does not get re-read when hardware is swapped.\n\n**Endurance is missing.** No wear, no written-bytes total, no power-on hours, no media-error count — no exporter here produces them. NVMe reports those over an admin ioctl that needs elevated privileges; temperature is the only health value the kernel publishes through sysfs. Tracked as **#549**. Do not read a green top row as a healthy drive.\n\nCeph does record wear, but only inside its own devicehealth module and not in Prometheus: `kubectl -n rook-ceph exec deploy/rook-ceph-tools -- ceph device ls`. It covers OSDs and nothing else, and a drive removed from Ceph is purged from that registry — its history goes with it, so the wear figure of a retired drive is not recoverable after the fact.\n\n**Roles are assigned in configuration, not by device name.** Talos selects the system disk and the EPHEMERAL volume by serial, Rook selects the OSD by `/dev/disk/by-id` path. Two consequences outlive any particular set of drives: a broad selector such as `disk.transport == 'nvme'` matches every drive in the box, with the installer taking the OSD as the failure mode — and a drive retired from Ceph is not necessarily out of service, so the drive with the least endurance left can be the one carrying container state.\n\n**A dying NVMe here hangs rather than errors.** Talos boots with `nvme_core.io_timeout=4294967295`, so NVMe commands never time out. Expect a stall, not an I/O error, and expect the latency panel to go flat rather than spike.\n\n**Kernel messages are not retained.** Talos kernel logs do not reach Loki — the only log jobs are Kubernetes pods and a systemd-journal from elsewhere. `talosctl -n <node> dmesg` is the only source, it is a ring buffer, and a reboot empties it. An NVMe error from before the last reboot left no trace anywhere.",
+        "content": "### What this dashboard cannot tell you\n\nThese notes are about mechanisms, not about the drives currently fitted. The inventory table above is the live answer to what is in the machines; nothing here restates it, because prose does not get re-read when hardware is swapped.\n\n**Wear is a budget, not a prediction.** The percentage is what the drive reports against its own rated endurance. Drives do not stop at 100 — they usually keep working and start consuming spare blocks — so read it for planning, and read available spare and media errors for whether something is failing now. Those are different questions and the alert rules treat them as such.\n\n**A green top row is not a healthy drive.** Endurance says nothing about the drive that dies of a controller fault tomorrow, and this dashboard cannot see one coming.\n\nCeph keeps its own wear figures for OSDs in the devicehealth module, which is a useful cross-check but covers OSDs only: `kubectl -n rook-ceph exec deploy/rook-ceph-tools -- ceph device ls`. A drive removed from Ceph is purged from that registry and its history goes with it.\n\n**Roles are assigned in configuration, not by device name.** Talos selects the system disk and the EPHEMERAL volume by serial, Rook selects the OSD by `/dev/disk/by-id` path. Two consequences outlive any particular set of drives: a broad selector such as `disk.transport == 'nvme'` matches every drive in the box, with the installer taking the OSD as the failure mode — and a drive retired from Ceph is not necessarily out of service, and putting a worn one on EPHEMERAL is a sensible destination rather than a hazard — that volume is built to be rebuilt. Check the inventory table for what a given drive holds before reading its wear as urgent.\n\n**A dying NVMe here hangs rather than errors.** Talos boots with `nvme_core.io_timeout=4294967295`, so NVMe commands never time out. Expect a stall, not an I/O error, and expect the latency panel to go flat rather than spike.\n\n**Kernel messages are not retained.** Talos kernel logs do not reach Loki — the only log jobs are Kubernetes pods and a systemd-journal from elsewhere. `talosctl -n <node> dmesg` is the only source, it is a ring buffer, and a reboot empties it. An NVMe error from before the last reboot left no trace anywhere.",
         "mode": "markdown"
       },
       "title": "Gaps and caveats",