OpenBSD Advanced Installation: GPT UEFI Mirror

Important OpenBSD systems should be installed onto a pair of mirrored disks so that malfunction of a single disk won't shut down services and cause data loss. OpenBSD FAQ has section about Installing to a Mirror which covers both MBR and GPT partitioning schemes. Seasoned admins familiar with OpenBSD's way of naming devices and tools such as fdisk and disklabel will find everything they need regarding mirrored setup there. This article adds a bit more information about installing OpenBSD to a mirror in newcomer friendly format.

Assuming we have sd0 and sd1 (SSDs), as well as sd2 (OpenBSD USB install media), we boot as usual and choose (S)hell when prompted.

We will manually create required disk devices for softraid setup, one for each device we currently have, and additional one for softraid device:

cd /dev
sh MAKEDEV sd0 sd1 sd2 sd3

Create GPT scheme on both our SSDs:

fdisk -gy -b 532480 sd0
fdisk -gy -b 532480 sd1

Invoke command-driven label editor to operate on first of two SSDs:

disklabel -E sd0

Create single partition of RAID FS type which spans whole disk:

sd0> a a
offset: [532544] 
size: [33021855] *
FS type: [4.2BSD] RAID
sd0*> w
sd0> q

Dump layout of sd0 to a file named layout, restore it to sd1, and remove file:

disklabel sd0 > layout                                                       
disklabel -R sd1 layout                                                      
rm layout      

Create mirror from newly created partitions on both SSDs:

bioctl -c 1 -l sd0a,sd1a softraid0

sd3 at scsibus2 targ 1 lun 0: <OPENBSD, SR RAID 1, 006>
sd3: 16123MB, 512 bytes/sector, 33021327 sectors
softraid0: RAID 1 volume attached as sd3

OpenBSD FAQ warns that vew device probably has a lot of garbage where master boot record and disklabel are expected, so zeroing the first chunk of it is highly recommended.

dd if=/dev/zero of=/dev/rsd3c bs=1m count=1

Type install to restart the installer:

install

Answer prompts as in standard install and choose appropriate device as root disk when asked:

Which disk is the root disk? ('?' for details) [sd0] sd3

Partition as in standard install, continue to the end of the install as usual and choose reboot when prompted.

After reboot check status of RAID volume (root or appropriate doas privileges are needed):

bioctl sd2

Volume      Status               Size Device  
softraid0 0 Online        16906919424 sd2     RAID1 
          0 Online        16906919424 0:0.0   noencl <sd0a>
          1 Online        16906919424 0:1.0   noencl <sd1a>

Confirm partitions are mounted from RAID volume:

# df -h

Filesystem     Size    Used   Avail Capacity  Mounted on
/dev/sd2a      988M    106M    833M    12%    /
/dev/sd2d      3.9G   18.0K    3.7G     1%    /home
/dev/sd2e      989M   10.0K    940M     1%    /tmp
/dev/sd2f      1.9G    1.3G    569M    70%    /usr
/dev/sd2g      989M    288M    652M    31%    /usr/X11R6
/dev/sd2h      989M    220K    940M     1%    /usr/local
/dev/sd2j      989M    7.9M    932M     1%    /var

Here's transcript of terminal session: