node_md_* does not show RAID syncing

Host operating system: output of uname -a

Linux barman-01 4.15.0-118-generic #119-Ubuntu SMP Tue Sep 8 12:30:01 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

node_exporter version: output of node_exporter --version

node_exporter, version 1.0.0 (branch: HEAD, revision: b9c96706a7425383902b6143d097cf6d7cfd1960)
  build user:       root@3e55cc20ccc0
  build date:       20200526-06:01:48
  go version:       go1.14.3

node_exporter command line flags

Excerpt from the systemd service:

[Service]
Type=simple
User=prometheus
Group=prometheus
ExecStart=/usr/local/bin/node_exporter \
  --web.listen-address=10.10.90.1:9100 \
  --collector.diskstats.ignored-devices='^(ram|loop|fd|(h|s|v|xv)d[a-z]|nvme\\d+n\\d+p)\\d+$' \
  --collector.filesystem.ignored-mount-points='^/(sys|proc|dev|run)($|/)' \
  --collector.netdev.device-blacklist='^lo$' \
  --collector.textfile.directory=/var/lib/prometheus/node_exporter \
  --collector.netstat.fields='(.*)' \
  --collector.vmstat.fields='(.*)' \
  --collector.interrupts \
  --collector.processes \
  --collector.systemd \
  --collector.tcpstat

Are you running node_exporter in Docker?

No.

What did you do that produced an error?

metrics:

root@barman-01 ~ # curl -Ss 10.10.90.1:9100/metrics|grep _md_
# HELP node_md_blocks Total number of blocks on device.
# TYPE node_md_blocks gauge
node_md_blocks{device="md0"} 1.046528e+06
node_md_blocks{device="md1"} 1.9530507264e+10
# HELP node_md_blocks_synced Number of blocks synced on device.
# TYPE node_md_blocks_synced gauge
node_md_blocks_synced{device="md0"} 1.046528e+06
node_md_blocks_synced{device="md1"} 1.9530507264e+10
# HELP node_md_disks Number of active/failed/spare disks of device.
# TYPE node_md_disks gauge
node_md_disks{device="md0",state="active"} 4
node_md_disks{device="md0",state="failed"} 0
node_md_disks{device="md0",state="spare"} 0
node_md_disks{device="md1",state="active"} 4
node_md_disks{device="md1",state="failed"} 0
node_md_disks{device="md1",state="spare"} 0
# HELP node_md_disks_required Total number of disks of device.
# TYPE node_md_disks_required gauge
node_md_disks_required{device="md0"} 4
node_md_disks_required{device="md1"} 4
# HELP node_md_state Indicates the state of md-device.
# TYPE node_md_state gauge
node_md_state{device="md0",state="active"} 1
node_md_state{device="md0",state="inactive"} 0
node_md_state{device="md0",state="recovering"} 0
node_md_state{device="md0",state="resync"} 0
node_md_state{device="md1",state="active"} 1
node_md_state{device="md1",state="inactive"} 0
node_md_state{device="md1",state="recovering"} 0
node_md_state{device="md1",state="resync"} 0

mdstat:

root@barman-01 ~ # cat /proc/mdstat
Personalities : [raid1] [raid6] [raid5] [raid4] [linear] [multipath] [raid0] [raid10]
md1 : active raid6 sdb2[1] sdc2[2] sdd2[3] sda2[0]
      19530507264 blocks super 1.2 level 6, 512k chunk, algorithm 2 [4/4] [UUUU]
      [==============>......]  check = 73.4% (7173181200/9765253632) finish=273.0min speed=158203K/sec
      bitmap: 2/73 pages [8KB], 65536KB chunk

md0 : active raid1 sdb1[1] sdc1[2] sdd1[3] sda1[0]
      1046528 blocks super 1.2 [4/4] [UUUU]

unused devices: <none>

What did you expect to see?

I expected to see difference between node_md_blocks and node_md_blocks_synced values. Currently values are the same although /proc/mdstat shows syncing.

node_md_blocks{device="md1"} 1.9530507264e+10
node_md_blocks_synced{device="md1"} 1.9530507264e+10

I expected recovering and resync metrics set to 1:

node_md_state{device="md0",state="recovering"} 0
node_md_state{device="md0",state="resync"} 0

Start by reproducing the discrepancy at the node_exporter /metrics endpoint while comparing it with /proc/mdstat during an active RAID check or sync. Trace how the md metrics are derived and verify that node_md_blocks_synced and the recovering/resync states reflect the active operation; done means the exported values match /proc/mdstat.