One system and Two system upgrade in EM 12c

One System Upgrade:

•           This approach is simpler.
•           This approach assumes the same host as the prior version of operation.
•           The repository components are upgraded in the same repository database.
•           This approach is suitable, when the number of agents is less.
•           Requires downtime.
•           OMA , OMS and Repository database are upgraded at once.

Two System Upgrade:

•  This approach is useful in more complex monitoring environments, where:
•   A different host from the prior OMS version of operation will be used.
•  The repository components will be upgraded in a different repository database copy.
•  Best suited for large agent counts and anywhere the unmonitored time must be minimized.
•   Minimal Downtime
•   The existing reports, metrics and jobs are migrated as well.