SAP S/4HANA Migration Cockpit Overview
When setting up SAP S/4HANA Cloud for a customer, an important task is migrating all required business data from their legacy (old) database(s) to the target application layer (on SAP HANA). The SAP S/4HANA Migration Cockpit is a tool that provides multiple methods of migrating data from as many legacy systems, SAP or non-SAP, as needed. You open the Migration Cockpit from an app called Migrate Your Data on the Fiori launchpad, as long as you have the permission assigned to access the application (see here). This same app is available in all deployments of SAP S/4HANA - on premise, private cloud, and public cloud - although the functionality and migration object template availability may be slightly different by deployment.
The SAP S/4HANA Migration Cockpit is an embedded tool - there is no additional cost to use it. The tool has a comprehensive library of migration object templates with the necessary fields already defined to help you migrate data to the SAP HANA application layer. It automatically maps source data from the templates to the SAP S/4HANA target system and guides you through a series of step-by-step activities to confirm the mappings and finalize migration, with validation checks occurring in the background.
The SAP S/4HANA Migration Cockpit is designed to be used during a period of time when large volumes of data need to be moved from other system(s) to the target system. This always is necessary during implementation of SAP S/4HANA Cloud, but could also be relevant if a customer who has already gone live with SAP S/4HANA Cloud acquires a subsidiary organization and needs to move data from the subsidiary's database(s) to the parent company's SAP HANA application layer.

Permission to Migrate Data
In addition to having permission to access the Migrate Your Data app, you need permission to migrate each type of data. This is because the Migration Cockpit tool uses the same APIs and technical checks that would be done if you were to create a new data value through the respective application. For example, if I need to create a new bank record in my system, I would use the application, Manage Banks - Master Data. The app would present me with several fields capturing information about the new bank to create the record in my system.
Now if I need to create 1,000 banks, it wouldn't be feasible to create each through the Manage Banks - Master Data app one-by-one. Instead, I would use the Migrate Your Data app to facilitate creating all 1,000 bank records at one time. After migrating all bank records, I would check the Manage Banks - Master Data app to verify the banks I've migrated are now available. Therefore when we migrate data, we need permission to access both the Migrate Your Data app, and the app we'd use to create that data as a one-off. All migration objects available in SAP S/4HANA Cloud are documented in the SAP Help Portal here. Each migration object lists the app required to validate your data in the system in the Post-Processing section. When you click the link of this app, you are brought to the app information in the SAP Fiori Apps Reference Library, where the business role required to access the app is listed.

Note
To create one-off master data, use the relevant Master Data Script from SAP Process Navigator → SAP Best Practices for SAP S/4HANA Cloud Public Edition (latest release) → Accelerators → Implementation tab → Create your own master data
Methods of Migration
The SAP S/4HANA Migration Cockpit facilitates moving data to SAP S/4HANA Cloud through two different methods:

Migrate Data Using Staging Tables
A migration object template is filled and the data from the template is transferred first to a "staging table" (temporary table), then moved to the target SAP HANA application layer connected to the SAP S/4HANA Cloud system. Migration object templates can be filled through two different procedures:
- Local SAP S/4HANA Database Schema: You download the template in XML or CSV format (both can be opened in Microsoft Excel) and copy-paste or manually type data into each field. This is the most commonly used method, however it can be time consuming with large volumes of data.
- Remote SAP HANA Database Schema: A separate SAP HANA database is deployed and used as the "middle-man" between the customer's legacy database(s) and the target SAP S/4HANA Cloud system. An integration must be set up to connect the remote SAP HANA database to the target SAP S/4HANA Cloud system, and the customer is responsible for designing their own ETL (extract, transform, load) code or using SAP Data Services to move data from their legacy database(s) to the remote SAP HANA application layer. This method requires more time to initially set up, but can be more efficient for large volumes of data.
Note
Both procedures are documented in SAP Process Navigator: Data Migration to SAP S/4HANA from Staging (2Q2)Migrate Data Directly from SAP System
A Remote Function Call (RFC) connection is set up between an SAP ERP system on a compatible release and the target SAP S/4HANA Cloud system. Through the RFC connection, the source data is automatically converted to the SAP S/4HANA data model when loading data to the SAP S/4HANA Migration Cockpit.
Note
This method is documented in SAP Process Navigator: Data Migration to SAP S/4HANA from SAP (BH3)