node_exporter: Add physical host disk monitoring

roles/node_exporter/files/md_info.sh

@@ -0,0 +1,59 @@
+#!/usr/bin/env bash
+
+set -eu
+
+for MD_DEVICE in /dev/md/*; do
+  if [ -b "$MD_DEVICE" ]; then
+  # Subshell to avoid eval'd variables from leaking between iterations
+  (
+    # Resolve symlink to discover device, e.g. /dev/md127
+    MD_DEVICE_NUM=$(readlink -f "${MD_DEVICE}")
+
+    # Remove /dev/ prefix
+    MD_DEVICE_NUM=${MD_DEVICE_NUM#/dev/}
+    MD_DEVICE=${MD_DEVICE#/dev/md/}
+
+    # Query sysfs for info about md device
+    SYSFS_BASE="/sys/devices/virtual/block/${MD_DEVICE_NUM}/md"
+    MD_LAYOUT=$(cat "${SYSFS_BASE}/layout")
+    MD_LEVEL=$(cat "${SYSFS_BASE}/level")
+    MD_METADATA_VERSION=$(cat "${SYSFS_BASE}/metadata_version")
+    MD_NUM_RAID_DISKS=$(cat "${SYSFS_BASE}/raid_disks")
+
+    # Remove 'raid' prefix from RAID level
+    MD_LEVEL=${MD_LEVEL#raid}
+
+    # Output disk metrics
+    for RAID_DISK in "${SYSFS_BASE}"/rd[0-9]*; do
+      DISK=$(readlink -f "${RAID_DISK}/block")
+      DISK_DEVICE=$(basename "${DISK}")
+      RAID_DISK_DEVICE=$(basename "${RAID_DISK}")
+      RAID_DISK_INDEX=${RAID_DISK_DEVICE#rd}
+      RAID_DISK_STATE=$(cat "${RAID_DISK}/state")
+
+      DISK_SET=""
+      # Determine disk set using logic from mdadm: https://github.com/neilbrown/mdadm/commit/2c096ebe4b
+      if [[ ${RAID_DISK_STATE} == "in_sync" && ${MD_LEVEL} == 10 && $((MD_LAYOUT & ~0x1ffff)) ]]; then
+        NEAR_COPIES=$((MD_LAYOUT & 0xff))
+        FAR_COPIES=$(((MD_LAYOUT >> 8) & 0xff))
+        COPIES=$((NEAR_COPIES * FAR_COPIES))
+
+        if [[ $((MD_NUM_RAID_DISKS % COPIES == 0)) && $((COPIES <= 26)) ]]; then
+          DISK_SET=$((RAID_DISK_INDEX % COPIES))
+        fi
+      fi
+
+      echo -n "node_md_disk_info{disk_device=\"${DISK_DEVICE}\", md_device=\"${MD_DEVICE_NUM}\""
+      if [[ -n ${DISK_SET} ]]; then
+        SET_LETTERS=({A..Z})
+        echo -n ", md_set=\"${SET_LETTERS[${DISK_SET}]}\""
+      fi
+      echo "} 1"
+    done
+
+    # Output RAID array metrics
+    # NOTE: Metadata version is a label rather than a separate metric because the version can be a string
+    echo "node_md_info{md_device=\"${MD_DEVICE_NUM}\", md_name=\"${MD_DEVICE}\", raid_level=\"${MD_LEVEL}\", md_metadata_version=\"${MD_METADATA_VERSION}\"} 1"
+  )
+  fi
+done