Classic plans iteration-based scheduling (Scrum)
On an iteration-based scheduling, stories and their work stages are scheduled into defined iteration lengths. These can be either manually entered as fixed sprints, or you can allow Portfolio for JIRA to dynamically schedule them based on available resources, release dates and scope.
If you schedule work that contains different stages, the exact stages completion order is not relevant, only what fits in the overall sprint matters.
Scheduling stories
Story scheduling is dynamically forecasted depending on sprint length, available resources and release dates, unless you have configured fixed sprints for individual teams. Fixed sprints are set for a team with a beginning and end date and are used and give you an additional way to match how your team works in the real world with your plan. See Releases, teams and member assignments for more information.
Scheduling epics
Epics can act as grouping elements for stories or if they don't have child stories associated, they can be directly scheduled as work items. This makes the scheduling of epics different in these two cases:
Minimum load configuration
Stories are always filled as a whole into a sprint. If the full story does not fit in, it gets pushed into the next sprint.
For epics, in order for the schedule to be realistic, in most cases it is desired to resemble this behavior. That's what the minimum load setting is designed for.
Example: Several stories are scheduled first and epic 2 is scheduled for the last two sprints.
Looking at the releases/capacities view reveals that there would have been free capacities in sprint 2. However, the configured minimum workload is 5 days, so the item is not scheduled in a smaller increment.
How to turn the minimum load constraint off
When turning this constraint off, we see that the epic is scheduled to fill up any free capacities also in earlier sprints.
This results in a higher resource utilization, but might not necessarily reflect reality. If there is half a day left in a sprint, would you really start partial work for an epic?
Still, depending on how you use epics, there are situations where it is helpful to turn off this constraint, and maximize capacity utilization.
Fixed Sprints
All of the examples above show dynamic scheduling of work based on the information you have entered into your plan. Scrum teams can also have fixed sprints assigned to them (in the Sprint menu in the backlog) giving you more flexibility when scheduling. Fixed sprints allow you to set begin and end dates that a team will be working in a specific sprint which can be different from a team's typical cadence. See Working with Teams and Members for more information on setting up Fixed Sprints.