questions regarding -c option to gjournal label

[Abner Gershon]

By way of intro I am new to freebsd and am in the process of setting up a
small office server. I am leaning toward UFS with gjournal rather than ZFS
and would like to make UFS as stable as possible and obtain the best
possible data integrity.

The man page states, " *-c* Checksum journal records."

My questions are:
1. What are the journal records checksummed against? eg checked against
kernel cache? data provider record?
2. Is this an ongoing process for the duration of the journal or a one time
event?
3. What happens if checksum does not match?

Thanks in advance.

-Abner