Excellent reply JustaDBA.

Dumb question - How do you increase the size of your rollback segments? The scripts we have to create ours (historically) only contain initial and next extent storage options. i.e., there is no size value.
So we have 8 rollback segments created as

create public rollback segment rb1 storage(initial 1M next 1M)
tablespace rollback_data;
create public rollback segment rb2 storage(initial 1M next 1M)
tablespace rollback_data;