I recently had a disk fail on a system, which I found out from errors in dmesg. (blk_update_request: critical medium error)

I wanted to set up some alerts on prometheus so I could get notified the next time the same thing happens but couldn't find any metric from node exporter on the machine that indicated anything was wrong. The only disk error related metric I found is node_filesystem_device_error, which just returns the errors returned from the statfs syscall.

I went digging around in sysfs on the machine and found data about ext4 filesystem errors in these files:

• /sys/fs/ext4/<partition>/errors_count: number of ext4 errors (commit)
• /sys/fs/ext4/<partition>/warning_count: number of ext4 warning log messages (commit)
• /sys/fs/ext4/<partition>/msg_count: number of other ext4 log messages

...and SCSI disk errors in these files (hexadecimal):

• /sys/block/<disk>/device/ioerr_cnt: number of SCSI commands that completed with an error
• /sys/block/<disk>/device/iodone_cnt: number of completed or rejected SCSI commands

I think node exporter should export these metrics. Maybe somewhat like this:

# HELP node_ext4_errors Number of ext4 filesystem errors.
# TYPE node_ext4_errors counter
node_ext4_errors{device="/dev/sda1"} 123
# HELP node_ext4_warnings Number of ext4 filesystem warning messages.
# TYPE node_ext4_warnings counter
node_ext4_warnings{device="/dev/sda1"} 456
# HELP node_ext4_messages Number of ext4 filesystem messages.
# TYPE node_ext4_messages counter
node_ext4_messages{device="/dev/sda1"} 78
# HELP node_disk_ioerr_total Number of SCSI commands that completed with an error.
# TYPE node_disk_ioerr_total counter
node_disk_ioerr_total{device="/dev/sda"} 1000
# HELP node_disk_iodone_total Number of completed or rejected SCSI commands.
# TYPE node_disk_iodone_total counter
node_disk_iodone_total{device="/dev/sda"} 9999