Overview

This error occurs on VMware-hosted rXg virtual machines when the VM boot firmware setting (BIOS vs. EFI) does not match the option that was selected during the FreeBSD/rXg installation.

Problem / Question

• VM fails to boot
• Console displays ZFS i/o error and "can't read MOS of pool zroot"

Root Cause

The VM boot firmware type (BIOS or EFI) was changed after installation, or differs from what was used during the initial install. ZFS partition layout depends on the firmware type, so a mismatch prevents the bootloader from reading the pool.

Resolution

1. Power off the VM
2. In vSphere/ESXi, navigate to VM Options > Boot Options > Firmware
3. Set the firmware to match the option used during the original rXg installation (typically EFI for modern installs)
4. Power on the VM