Ever ran into issues using sysupgrade on OpenBSD because /usr ran out of space? OpenBSD developers are trying to address this issue.
Firstly, Stuart Henderson (
↫ OpenBSD Journalsthen@) modified the installer to increase free space prior to installing. […] Theo de Raadt (deraadt@) modified sysupgrade(8) so that, if space is too tight, it will fail gracefully rather than risk leaving the administrator with a broken system.
These are very welcome additions.

Coming back to OpenBSD after many years, installed it on my spare laptop. So far so good, but I always used custom partition scheme – just “a” for the system, maybe another one for swap and MAYBE /usr or /var. Things have changed. Apparently we now have experimental Wayland and VMs, which is wild to me. I remember the times when I couldn’t play flash videos and had to download them, because of flash plugin, LOL.
In times of ZFS and APFS, it is very strange to hear about space problems on some single partition.
I’m not sure ZFS is supported on OpenBSD. To be fair, my BSD experience is mostly FreeBSD (and clones like PlayStation, but I don’t think that count).
ZFS doesn’t like being full either.
You are probably right, but with zfs you don’t need to decide the size of a zvol on system install. so as long as there is space left in the zpool you can just set the quota for the particular zvol, no need to fuss arround with partitions tha meby cant be expanded