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DMO with system move with shd rep on target DB

Readers of this blog post should be familiar with the approach “DMO with system move”, as introduced in this blog https://blogs.sap.com/2017/05/22/dmo-with-system-move-the-use-case-to-change-pas-host-during-dmo/

Shadow repository always created on target database

SUM 2.0 meanwhile creates the shadow repository always on the target database. The approach was introduced in this blog https://blogs.sap.com/2019/09/09/dmo-shadow-repository-on-target-database-for-conversion-to-sap-s4hana-1909/ and is now used for all migration scenarios (with SUM 2.0 SP 08 and higher; but not with SUM 1.0). All migration scenarios means: it is not depending on the target product release, and it is not depending on the target database type. So this approach even applies for a move from SAP ECC 6.0 EHP 7 on SAP MaxDB (on-premise) to SAP ECC 6.0 EHP 8 on SAP HANA DB in a cloud infrastructure like SAP HANA Enterprise Cloud (HEC).

No shadow in source landscape for DMO with system move

For “DMO with system move”, the consequence is that on the source landscape, no shadow operations happen. There is no shadow repository created on the source database, and no shadow instance created on the source Application Server host (on which you have started the SUM).

The following figure illustrates this.

Shadow repository is created on target database

Changes for the approach DMO with system move

This approach (shadow operations only on target landscape) has a couple of implications:

  • SPAU/SPDD happen in target landscape
  • SUM will only allow the specification of the shadow instance number in target landscape (if expert mode is selected)
  • The shadow operations (creating shadow instance, shadow repository, …) happen in target landscape, and not necessarily in uptime – depending on the transfer mode selected, see below
  • Advantage of the approach is that shadow operations do not affect the source database performance

Strong recommendation to use parallel mode

The shadow operations happen on the target landscape, they take quite a while, and the transfer mode decides whether this is uptime or downtime for the source system.

The serial mode:

  • This is the transfer mode in which only one data transfer happens
  • You run the complete procedure on the source landscape until it is finished
  • This includes entering the downtime for the source system
  • Only then you copy the SUM folder from source to target
  • You start the SUM in the target and continue the procedure there
  • Only then the shadow operations run, which takes a while – in downtime!

The parallel mode:

  • This transfer mode is based on a continuous data transfer to target
  • You run the procedure in source until the dialog on phase HOSTCHANGE_MOVE_SOT
  • On this dialog (still uptime), you decide on parallel mode,
    so you start a synchronization, either manually or using the delivered script
  • Once the initial SUM folder is synchronized to the target, you start the SUM in the target
  • Still in uptime, the target SUM will execute the shadow operations in target
  • You run the source SUM until downtime dialog, but wait there until target SUM has finished shadow operations and is waiting to import dump files (phase EU_CLONE_MIG_DT_IMP)
  • Only then you enter downtime in source, so that creation of export files in source landscape runs parallel to import of dump files into target database

The following figure shows the point in time for which the source system is still in uptime, source SUM waits on downtime dialog (upper left browser window), whereas the target SUM is executing phase EU_CLONE_MIG_DT_IMP which is waiting for dump files to start the import (lower right window).

Parallel%20SUM%20execution%20in%20source%20and%20target

Parallel SUM execution in source and target

Boris Rubarth,
SAP SE, Product Management SUM

4 Comments
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  • Hello Boris,

    Thanks very much for providing a very useful information in this blog.

    How do we manually synchronize the dir in parallel data transfer esp when Source and target are on different OS e.g. Source is on HP-UX and target is RHEL.

    Right now SAP has provided a dmosystemmove.sh script but its only for Linux.. can we use custom script for data transfer between different OS? Does SAP support it?

    Thanks,

    Umesh PB

     

     

     

    • Based on my experience – you can customize the script.  you need to be careful that you’re copying the dump files in proper binary mode and have a method to verify complete copy (MD5 checking, etc).  I say this because I’ve done similar in the past with my own custom script.  Essentially my team replicated this DMO parallel move with earlier versions of SUM.

    • Hi Umesh,

      using the delivered script dmosystemmove.sh should be possible on all operating systems supporting rsync. I am not an expert on rsync, guess all Unix OS should work. For windows, I read that cygwin may be a way to use rsync, but I haven’t yet heard of anyone using this.

      Currently azcopy is not supported, as it creates the initial files in the target with final size already which makes SUM assume the file transfer is complete.

      Thank you Vijay to share your experience.

      Regards, Boris

  • Thanks Vijay, it helps.

    Meantime, I just tried to manually execute standard dmosystemmove.sh (which internally calls up rsync ) from HP-UX (In the DMO guide it says that this script is for Linux Only) and it works similar to Linux. I feel, only thing you might need to do is to setup the password less authentication e.g. for <sid>adm, between source and target and script would do its job of parallel transfer. I am planning to test this in upcoming  DMO run. Will share the outcome of the same.

    Thanks,

    Umesh B