Add per-source backup size breakdown to dashboard

- Update borgmatic-metrics script to collect size per source directory
- Add horizontal bar gauge panel showing backup size by source
- Sources: Pictures, Documents, devpi, Zettelkasten, Forgejo, Loki, PostgreSQL

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

ansible/roles/borgmatic_metrics/templates/borgmatic-metrics.sh.j2

@@ -125,6 +125,38 @@ borgmatic_last_archive_timestamp $last_timestamp
 # TYPE borgmatic_last_archive_duration_seconds gauge
 borgmatic_last_archive_duration_seconds ${last_duration:-0}
 EOF
+
+    # Collect per-source-directory sizes
+    cat >> "$TEMP_FILE" << 'EOF'
+
+# HELP borgmatic_source_size_bytes Size of each backup source directory in bytes
+# TYPE borgmatic_source_size_bytes gauge
+EOF
+
+    # List archive contents and group by source directory
+    $BORG_CMD list "${BORG_REPO}::${last_archive_name}" --format "{size} {path}{NL}" 2>/dev/null | awk '
+    {
+        size = $1
+        path = $2
+        # Map paths to friendly source names
+        if (path ~ /^Users\/[^\/]+\/Pictures/) { source = "Pictures" }
+        else if (path ~ /^Users\/[^\/]+\/Documents/) { source = "Documents" }
+        else if (path ~ /^Users\/[^\/]+\/devpi/) { source = "devpi" }
+        else if (path ~ /^Users\/[^\/]+\/code\/personal\/zk/) { source = "Zettelkasten" }
+        else if (path ~ /^Users\/[^\/]+\/.config\/borgmatic/) { source = "borgmatic_config" }
+        else if (path ~ /^opt\/homebrew\/var\/forgejo/) { source = "Forgejo" }
+        else if (path ~ /^opt\/homebrew\/var\/loki/) { source = "Loki" }
+        else if (path ~ /^borgmatic\/postgresql_databases/) { source = "PostgreSQL" }
+        else if (path ~ /^borgmatic\//) { source = "borgmatic_metadata" }
+        else { source = "other" }
+
+        totals[source] += size
+    }
+    END {
+        for (src in totals) {
+            printf "borgmatic_source_size_bytes{source=\"%s\"} %.0f\n", src, totals[src]
+        }
+    }' >> "$TEMP_FILE"
 fi
 
 # Atomic move

ansible/roles/grafana/files/dashboards/borgmatic.json

@@ -477,6 +477,53 @@
       "title": "Unique Chunks",
       "type": "stat"
     },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "prometheus"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "palette-classic"
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [{ "color": "green", "value": null }]
+          },
+          "unit": "decbytes"
+        },
+        "overrides": []
+      },
+      "gridPos": { "h": 8, "w": 8, "x": 16, "y": 4 },
+      "id": 14,
+      "options": {
+        "displayMode": "basic",
+        "minVizHeight": 10,
+        "minVizWidth": 0,
+        "orientation": "horizontal",
+        "reduceOptions": {
+          "calcs": ["lastNotNull"],
+          "fields": "",
+          "values": false
+        },
+        "showUnfilled": true,
+        "valueMode": "color"
+      },
+      "pluginVersion": "10.0.0",
+      "targets": [
+        {
+          "datasource": { "type": "prometheus", "uid": "prometheus" },
+          "expr": "topk(10, borgmatic_source_size_bytes)",
+          "legendFormat": "{{source}}",
+          "refId": "A"
+        }
+      ],
+      "title": "Backup Size by Source",
+      "description": "Breakdown of backup size by source directory",
+      "type": "bargauge"
+    },
     {
       "datasource": {
         "type": "prometheus",