Errata patches for vmd have been released for OpenBSD 6.4. Writing more than 4GB to a qcow2 volume corrupts the virtual disk.
Binary updates for the amd64 and i386 platforms are available via the syspatch utility. Source code patches can be found on the errata page: https://www.openbsd.org/errata64.html After patching, restart the vmd service.
