How about banks/brokers and their accounts data?
Primary and Secondary were running 24/7 with Secondary being in exact sync with Primary. If Primary or Secondary went down, Tertiary could be brought up in sync within 24 hours. Primary and Secondary were geographically separated (east/west coast). Tertiary was in the mid-west. After that, the additional facilities would take days to bring up, and then a bit of time to sync.
The specific bank is no longer alive as it was consumed by one of the "too big to fail" institutions.
The insanity of humanity all here on HN...