Zero Downtime Option for SAP S/4HANA Updates and Upgrades

Downtime is always key factor in updates or upgrades. Customers always ask to optimize the downtime to manage their business by increasing uptime of the SAP systems. SAP has introduce the Zero Downtime Option (ZDO) with SUM where no technical downtime required during updates and upgrades only application server restart required as part of cutover. ZDO has limitation as this option is not available with ECC to S/4HANA conversion. This article contains important viewpoint for Zero Downtime Option (ZDO) approach.

Overview of ZDO Approach

A technical system downtime during an update can be expensive. For this situation, the ideal solution would be to run an update without having a technical system downtime. With the ZDO of SUM, updates of ABAP applications can be run without a technical downtime and with a minimized business downtime.

The idea behind ZDO is to have a bridge-subsystem in parallel with the production system. During the update on the production system, users can continue their work on the bridge-subsystem. The bridge-subsystem reflects the source release and contains all data of the production system that users need to continue their work for example, working with transactions, scheduling, and running batch jobs, and running print requests.

High Level Overview on the Three Approaches

When comparing the three different approaches, you have to keep in mind that only the technical downtime is reduced. Also, the business downtime can be significantly reduced by using ZDO. The ZDO approach requires higher effort in terms of functional validation as well as project planning.

Approaches

                                                                Source : support.sap.com

Both, the standard approach, as well as the near-Zero Downtime Maintenance (nZDM) contain major improvements for minimizing the technical downtime. However, only with Zero Downtime Option (ZDO), can the technical downtime be reduced to a single restart of the application servers.

By choosing ZDO, all activities that formerly run as part of the technical downtime are moved into the phase so-called uptime on bridge where all users will be transferred to the bridge sub-system to proceed with their business operations.

The ZDO approach is beneficial for the following maintenance events:

  • Applying support package stacks
  • Applying feature packages
  • Customer system releases
  • System release upgrades

High Level Approach and Basic steps of the ZDOSource%20%3A%20support.sap.com

Source : support.sap.com

`The basic steps of the ZDO procedure are:

  1. Business users work on the original system on source release 1.
  2. Meanwhile, the uptime processing of SUM has been started.
  3. Once uptime processing finish, SUM will rollover the business users to the bridge subsystem.
  4. The bridge subsystem still represents the source release as the target release is yet to be finalized by SUM.
  5. The business users can continue with their work since the transition to bridge happens seamless.
  6. While the business continuous to work, the target release is finalized in parallel by SUM.
  7. During the maintenance procedure, transactional consistency is ensured.
  8. Both releases, source and target, are stored in the same database but the access happens via different database schemas.
  9. The cut-over and activation of the target release includes the following steps:
  • Perform Ramp-down activities at release 1 (Source) like remove dialog users, lock users, suspend batch jobs, cleanup tRFC/qRFC queues, and clean failed update processes.
  • Parallelized restart of all application servers by SUM. The database is not restarted.
  • Perform Ramp-up activities at release 2 (Target) which typically includes tasks like import of transports, functional validation, unlock users, re-scheduled batch jobs.

10. After the restart and ramp-up of the system, users will work on release 2 (Target).

General Prerequisites for ZDO:

Refer SAP Note 2707731 – Prerequisites and restrictions of Zero Downtime Option of SUM for SAP S/4HANA to check the latest prerequisites and restrictions like supported upgrade and update paths.

  • Using ZDO requires an educated employee who took the mandatory training ADM330 plus knowledge badge assessment ADM330K.
  • Not all add-ons available for SAP S/4HANA implicitly are equipped with zero-downtime maintenance capability. Hence, Software Update Manager is equipped with an automated check if ZDO can be used for the system. So, always check the latest version of SAP Note 2707731 which lists the not supported SAP and partner add-on products by ZDO.
  • It is important to understand that the path from SAP ERP to SAP S/4HANA is called System Conversion. ZDO is not possible for System Conversion. Instead, downtime-optimized Conversion or NZDT might be applicable approaches. For that, Please refer one of my colleague blog  https://blogs.sap.com/2022/05/24/downtime-optimized-conversion-for-sap-s-4hana-brownfield-conversion-to-reduce-downtime/.

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                                                                Source : support.sap.com

Let understand about how to use ZDO in SUM:

  1. ZDO comes along with SUM that is the standard tool for software maintenance. There is no additional license needed and no separate tool required.
  2. The database footprint is rather small since not the entire database is cloned. Instead, only selective tables are cloned. The cloned tables are determined based on the changes to be performed with the maintenance event.
  3. The technical downtime goes down to a single restart of the application servers. The database, however, isn’t restarted. Usually, the restart takes approximately 5 to 15 minutes depending on the number of application servers.

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  • In the very first dialog (step 1) you specify the stack.xml file which includes the information about the source and target release of the planned maintenance event.
  • Select the Scenario Strategy on the next dialog (step 2). If the dialog Scenario Strategy (step B) does not display the Zero Downtime Option (ZDO) approach, it might be that a component in the system is not ZDO enabled.
  • Next, the dialog (step 3) Authentication of Scenario asks you to provide the password generated by SAP

Let Understand about High Level SUM Operations with ZDO

      1. End Users Operating on the Original System

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At the beginning of the ZDO procedure, until phase REQ_USER_ROLLOVER_PREP is reached, the end users operate on the original system.

At the end of the pre-processing, SUM generates views in the bridge schema pointing to the tables stored in the original schema. For each table in the system (SAP-owned and customer created), a view is generated. For example, if there are 10000 tables in the original schema, 10000 views are also generated in the bridge schema.

At this point in time, only one version of the tables is present, the so-called V1, which represents the source release.

      2. End Users Operating on the Bridge Subsystem

zzThe rollover initiate to the bridge subsystem in technical phase REQ_USER_ROLLOVER_PREP. Work processes of all application servers are automatically reconnected to the bridge schema in  technical phase BRIDGE_RECONNECT. After transitioning all end users to the bridge subsystem, the default database schema of the production is shadow instance schema like SAPHANADBSHD.

The upgrade subsystem, which is used to finalize the upgrade, connects to the original database schema (like SAPHANADB).

While the upgrade is performed on the target release tables (V2 tables), the generated views in the bridge schema still point to the source release tables (V1 in this example). Tables that are either not changed by the upgrade or the structural change can be compensated by the database view does not require two versions of a table. These tables are available for both the bridge and upgrade subsystem.

All existing application servers of the system are reconnected to the bridge subsystem. End users do not have to logoff and logon as the transition from the original to the bridge database schema happens seamless triggered by the ABAP kernel in phase BRIDGE_RECONNECT.

      3. End Users Operating on the Target Releasezz

At the end of bridge runtime in technical phase REQ_USER_ROLLBACK_PREP, the system needs to be ramped down. As in every other upgrade this requires activities like:

  • cleanup of tRFC/qRFC queues
  • Suspend batch jobs
  • stop inbound and outbound interfaces
  • check for failed update processes
  • logoff all dialog users
  • lock users
  • etc

After the cut-over which is restarting the application servers and ramp up activities, the business users are connected back again to the original schema and the business operations can continue.

 Important Reference:

  • Guides for Zero Downtime Option with SUM 2.0
  • 2707731– Prerequisites and restrictions of Zero Downtime Option of SUM for SAP S/4HANA
  • 2163060 – Prerequisites and restrictions of Zero Downtime Option of SUM for SAP Business Suite
  • 2471883 – SUM Impact Analysis for ZDO
  • 2214409 – SAP S/4HANA: Compatible Add-Ons

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