After upgrading to 7.0 the system datastore was missing (attached via SATA). Related to this article https://jc-lan.org/2017/02/01/poor-performance-in-esxi-6-5-with-jetway-jnf9g-qm77/ I had previously disabled the built in (native) AHCI driver of ESXi due to poor performance. Enabling it again followed by a reboot of the host resolves the issue:
You can verify if any modules are disabled with the following command (in this case we are looking for vmw_ahci)
esxcli system module list | grep false
Re-enable it:
esxcli system module set --enabled=true --module=vmw_ahci
Then reboot