Relevent telegraf.conf

[[inputs.disk]]
  ignore_fs = ["tmpfs", "devtmpfs", "devfs", "overlay", "aufs", "squashfs"]

System info

Telegraf 1.12.1 running in Docker 20.10.8

Docker

services:
  telegraf:
    image: telegraf:1.21
    environment:
      HOST_PROC: /host/proc
      HOST_MOUNT_PREFIX: /host
    volumes:
      - ./telegraf.conf:/etc/telegraf/telegraf.conf
      - /:/host:ro
      - /sys:/host/sys:ro

Steps to reproduce

1. Update Telegraf to 1.21.1
2. Look at the disk metrics

Expected behavior

All disks (/dev/sda1 and /dev/sdb) should export data.

Actual behavior

Only data for /dev/sda1 is visible, /dev/sdb is missing.

Additional info

The diskio input plugin still reports data for /dev/sdb after the update to 1.21.1, only disk is missing data. I've tried the Troubleshooting instructions and both expected disks (/dev/sda1 and /dev/sdb) show up in the Docker container as a mount under /host with an ext4 filesystem and stat succeeds for both.

Downgrading the Docker image to 1.20.4 fixes the issue and /dev/sdb has data again. There's no 1.21.0 image I could test with but data stopped being available after the upgrade from 1.21.0 to 1.21.1.