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an adequate choice of a migration method are just as important as the
migration itself. Some of the steps below cab be undertaken very early,
parallel to strategic considerations and the selection of the Cloud provider.
Selecting a mode of migration
Fundamentally, depending on the size of the company and service, the
following different migration forms are available.
Big Bang (moving in one step): In a big‐bang migration, the entire
service transfer is performed for all users at the same time. A
migration of this kind requires good planning and normally one or
two test migrations are adviseable. In particular, migration activities
that take a long time are critical in a Big Bang migration (e.g., copying
all files). The particular advantage of this migration variation lies in
the fact that no parallel system usage is necessary. The Big Bang
migration is used where using parallel systems would be costly and
organisationally difficult to carry out.
Step‐by‐step migration: A phased migration is carried out in several
steps. In the individual steps, specific groups of users are migrated.
The complexity can easily be controlled with the size of these steps.
During the entire migration, parallel services must be maintained.
The steps are carried out in the same form, i.e. with each step the
migration team gains more experience and the quality of the
migration thus rises.
Optional pilot operation: Pilot operation can be used both before a
Big Bang migration as well as before a step‐by‐step migration. In this
phase, the service is provided for a particularly "skilful" group of
users. Helpful insights for the migration are identified based on the
experience of these pilot users. The insights gained flow into the
documentation, as well as into the technical migration procedure.
The choice of the migration method should be made as early as possible.
Those responsible for the choice should seek advice from both the Cloud
provider as well as internal and external experts. For each Cloud service
there are insights as to what has previously worked well and what has not.
Once the mode of migration has been set, the decision whether to run an
optional pilot operation needs to be made. Pilot operations should be
designed in such a way that the users really use the new service instead of
the old service. Use in addition to the existing service has not proven to be
particularly helpful.
