Migrating the primary hard drive in OpenBSD

My web server is running on an OpenBSD VM that had to be upgraded from 7.7 to 7.8, but it turned out that the default OpenBSD drive labels created with disklabel(8)’s -A option made the /usr partition on the 16GB big drive too small to automatically update with sysupgrade(8).

After having looked around a bit for some way to still do this, I first stumbled upon sysclean(8). While nice, it didn’t help as there were essentially no files I could delete from /usr without bricking the system, so I was looking for another solution.

Eventually I stumbled over the blog post Cloning and Migrating the Primary Hard Drive on an OpenBSD Install which gives instructions on how to clone the primary hard drive in OpenBSD.

After following the instructions, which guides you through partitioning of the new disk, setting up labels and copying the live distro with dump(8) and restore(8), I managed to get my system up and running with a bigger drive that allowed me to run sysupgrade(8), syspatch(8) and upgrade all the packages with pkg_add(1).

There was one instance where I deviated from the blog post, though. Instead of taking the old partitions from disklabel(8) and applying them to the new disk, I generated new partitions with disklabel -wA.

Just don’t do the same mistake I did: Don’t forget to write a default MBR to the disk with fdisk -i before doing anything else. OpenBSD will boot, but things will be broken.