Downtime-Optimized DMO

Overview

The downtime-optimized DMO procedure performs a part of the data migration in the uptime processing. This technique significantly reduces the overall business downtime. The delta record and replay technology (CRR) ensures that any changes, which users made in the uptime but during the data migration, are considered.

In the following, you get a rough overview of the new approach and the difference to the standard DMO procedure:

The downtime-optimized DMO in a nutshell:

Determined large application tables are already migrated during the uptime in phase EU_CLONE_MIG_OPTDMO_RUN. Changes to these tables are recorded after their migration.
A delta migration is carried out during the uptime in phase RUNASYN_RRC_REPLICATE. If necessary, a second delta migration takes place during the downtime in phase RUN_RRC_REPLICATE_FINAL. The delta migrations depend on the change rate of the users.
Afterwards during the downtime, the remaining tables are migrated in phase EU_CLONE_MIG_DT_RUN.

Prerequisites and Restrictions

For further the prerequisites and restrictions concerning downtime-optimized DMO, see section I/ Important General Information of the related SAP Note for the DMO that is mentioned in Required SAP Notes.

Enabling and Monitoring

To enable and monitor the downtime-optimized DMO, proceed as follows:

After the start of the Software Update Manager, the initial dialogs to specify the scenario and the roadmap appear. Choose the scenario category with stack.xml configuration file.
If a database migration to SAP HANA database is not mandatory anyway, choose in the dialog Decision on DMO the database migration to SAP HANA.
In a further dialog, select the scenario strategy downtime-optimized.
Sometime afterwards, the dialog Migration Parameters appears in which you specify the path and name of the file with the table names that are to be migrated during the uptime. The list must be a plain text file with one table name per line.
At the end of the uptime, that is at the end of the Preprocessing roadmap step, you can check the status in the CRR Control Center of the SUM Utilities. The dialog Preparations for Downtime in phase DOWNCONF_DTTTRANS offers a link to it.

Table Selection

For various reasons, the table size as only criterion for the manual table selection is not always clear:

The table migration duration is not always linear to the table size.
You cannot include all tables. For more information, see SAP Note 2547309 .
The change rate is relevant. Therefore, it is recommended to consider tables with a high change rate only when needed to meet the downtime requirements.

To meet the requirements for the table selection, use the tool Uptime Table Selection for downtime-optimized DMO of the SUM Toolbox at the end of a DMO run on a sandbox system. The tool can be used in any system. If you run the tool on a system where a SUM run with DMO or downtime-optimized DMO has been completed, the tool automatically selects the required files from the DIR_PUT directory. Otherwise, the input files must be provided manually.

For more information about the installation of the SUM Toolbox, see SAP Note 3092738 Information published on SAP site and the SAP Notes referenced in it.

Impact Analysis

Changes on the content of those tables that are migrated already during uptime must be recorded by means of triggers. However, the change recording increases the daily database growth.

To avoid a business impact on your production system, it is necessary to estimate in advance how much additional database space is required. The Impact Analysis approach provides you with an estimation for this.

For more information, see the SAP Notes 2402270 Information published on SAP site and 2481983 .