Upgrade to pfsense 2.3.1 in Hyper-v 2008 R2 failed - unbootable

[delusion]

After upgrade to 2.3.1 pfsense canot boot with error:

Mounting from ufs:/dev/ad0s1a failed with error 19.

[kpa]

The name of the root partition has probably changed to ada0s1a, try entering ufs:/dev/ada0s1a at the prompt.

[delusion]

the right solution is here:

https://forum.pfsense.org/index.php?topic=109952.msg613371#msg613371