Using smartctl is widely described on the web for Linux and FreeBSD based environments, but it may be non-trivial in OpenBSD case.
This is because all of the disk operations are mostly inherited from 4.2BSD operating system.
As the usuals: partitions, filesystems and labeling are excellently described in OpenBSD Handbook I won’t cover that in following article.

Installation of smartmontools in OpenBSD 6.6

smartctl used for reading the S.M.A.R.T status of given storage device is fairly easy to install as it is a part of smartmontools package. All of the following commands are executed with root privileges.

mainframe# pkg_add smartmontools
quirks-3.183 signed on 2020-03-22T11:47:19Z
smartmontools-7.0p0: ok
The following new rcscripts were installed: /etc/rc.d/smartd
See rcctl(8) for details.

Next step is to enable the smartd daemon that monitors the devices.

mainframe# rcctl enable smartd

Now the smartd should be added to rc.conf.

mainframe# cat /etc/rc.conf.local | grep smartd | wc -l

Finally we can run smartd without rebooting the machine.

mainframe# rcctl start smartd

Three letters to rule it all

A key to running on the device of your choice is to know how OpenBSD mounts partitions in /dev. IDE devices are usually mounted with wd prefix, and SCSI devices with sd prefix. A key to run the smartctl tool is to know what each suffix letter stands for:

  1. a: the root partition of given disk,
  2. b: usually swap,
  3. c: whole disk - raw access.

The latter is to be used with smartctl tool.

Example run

mainframe# smartctl -i /dev/sd0c
smartctl 7.0 2018-12-30 r4883 [x86_64-unknown-openbsd6.6] (local build)
Copyright (C) 2002-18, Bruce Allen, Christian Franke,

Device Model:     INTEL SSDSC2KW128G8
Serial Number:    …
LU WWN Device Id: 5 5cd2e4 14f724e80
Firmware Version: LHF002C
User Capacity:    128,035,676,160 bytes [128 GB]
Sector Size:      512 bytes logical/physical
Rotation Rate:    Solid State Device
Form Factor:      2.5 inches
Device is:        Not in smartctl database [for details use: -P showall]
ATA Version is:   ACS-3 (minor revision not indicated)
SATA Version is:  SATA 3.2, 6.0 Gb/s (current: 3.0 Gb/s)
Local Time is:    Sun Mar 22 23:57:21 2020 CET
SMART support is: Available - device has SMART capability.
SMART support is: Enabled

smartd status in the log

By default smartd polls the devices every 30 min and outputs its status in the /var/log/daemon log.