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Create a Consistent Copy of Your Entire SAP Landscape — Without Taking Systems Offline

by Jochen Wolter | SAPinsider

July 1, 2003

by Jochen Wolter, SAP AG SAPinsider - 2003 (Volume 4), July (Issue 3)
 

Consistency Technologies Offer Alternatives to Multiple Single-System Backups

Business processes from mySAP Business Suite (which spans financials, CRM, SCM, and BI, among others) increasingly cover multiple components and systems. Consider a process like business partner management in mySAP CRM, which exchanges data between two or more systems running on different servers. When implementing such landscapes, customers often face the requirement of creating a consistent image1 of the entire landscape — what I will refer to as a consistent landscape image — for use as a backup or for building a consistent test environment. However, constant cross-system exchange of information makes preserving data consistency a challenge when trying to create a landscape image, particularly if you require 24x7 availability. Achieving data consistency among different systems is no problem if all the systems can be brought down for backup, but creating consistent landscape images during online operation may require a different approach than the single-system online backups that had been sufficient in the past.

A practical solution has emerged by looking beyond the application level for data synchronization and, instead, considering a consistent landscape image based on split-mirror technology.2 No matter what systems — or how many — your processes use, they all ultimately store their data in a storage system.3 And more important, all the information needed for data exchange (RFC tables4) is also stored there.

So if consistency of data is your prime consideration, and availability is critical, your storage system can serve as a point of synchronization for cross-system data. Combined with the fault-tolerant RFC protocol, this approach allows you to preserve data consistency for an image taken of all systems simultaneously.

In fact, this technology has already been a success in tests specifically for SAP environments. SAP and its hardware partners have recently tested methodologies for creating a consistent image of a federated system landscape using the “consistency technology” currently available from select storage systems (see “Federated Backup Project” below). The result was a consistent image of data for the entire test landscape, making this an important consideration for any customer evaluating backup and recovery needs.

The Federated Backup Project: Testing Consistency Technologies at Work

One goal of the Federated Backup Project was to show, in cooperation with our hardware partners, that consistency technologies work in an SAP environment. We developed a methodology to simulate business processes exchanging data between multiple systems of our test landscape, and to verify this test data for consistency. With a test tool designed by SAP for this purpose, we ran a high RFC communication workload while creating an image of the landscape with and without consistency technology. We started a second landscape on this image, and found that only with the use of consistency technology were we able to create a landscape image that was in a consistent state.

The complete test setup and results can be found at http://service.sap.com/atg -->Backup and Restore - ->Federated Backup.

Uses for a Consistent Landscape Image
A consistent landscape image can be used to set up a test landscape, for example, for a quality assurance system or for upgrade testing. It can serve as a backup as well, to allow you to restore the complete production landscape to a point of consistency in the past (for example, in case of a disaster).

A consistent landscape image could also be used to restore individual systems if necessary due to a system or hardware error (including both complete or incomplete recovery) — albeit with some important limitations.5 So before you go ahead and completely replace existing backup strategies, be sure to determine whether all restore and recovery options are supported by the respective technology!

NOTE:
Backup Consolidation, which means replacing multiple, single-system backup strategies with a single process )i.e., the creation of a consistent landscape image as a backup) can reduce cost and administrative work, while providing the additional option of restoring the complete landscape to these consistency points.

How Is a Consistent Landscape Image Created?

Consistency technology creates a synchronization point by momentarily holding I/Os on either the database level or the storage level, simultaneously, for all systems of the landscape. In this case, we’ll focus on two approaches tested in the Federated Backup Project:6

  • Consistent Split is an operation available from some third-party storage systems to create a consistent landscape image at the storage level — and requires only a single command. Consistent Split instantly holds I/Os for all relevant storage volumes while a split-mirror copy is generated. All storage volumes reflect exactly the same state, thus yielding a consistent image.

    This applies to volumes on a single storage system, but also can be extended for volumes located on multiple storage systems either by defining Consistency Groups — groups of storage volumes that can span multiple storage systems — or by coordinating Consistent Split operations from a dedicated host running consistency software.

  • Coordinated Suspend works by momentarily suspending I/O operations on all involved database systems (database suspend) while a split-mirror copy is taken for all related volumes. Coordinating these suspend operations and enclosing comprehensive error-handling procedures is the main challenge for implementing this solution.

Each method has strengths and drawbacks (see Figure 1 for a side-by-side comparison).

  Consistent Split Coordinated Suspend
Level Storage - no ntervention required at database or application level Database - no intervention required at application level
Implementation Considerations

Easy implementation and handling

No ready-to-run procedure available for this technology

Not available in all storage systems Complexity of implementation
Also conceivable without split-mirror technology
Uses for Resulting Landscape Image QA system

QA system

Test landscape

Test landscape

Restore of production in case of disaster (incomplete recovery of entire system landscape)

Restore of production in case of disaster (incomplete recovery of entire system landscape)

Restore and recovery of a single system
Benefits Ease of implementation

Single-system backup ("backup consolidation")

Almost imperceptible impact on production

Only short delay in production

Data consistency across entire landscape Data consistency across entire landscape
Drawbacks Currently no general support for single- system recovery (no "backup consolidation") Requires development, testing, and implementation of scripts to control complete operations
Requires possibly complex error-handling procedures
Figure 1 The Two Consistency Technologies At-a-Glance

Coordinated Suspend is an extension of the split-mirror backup procedure for single systems, and thus allows all types of single-system recoveries. This makes it an option for replacing all existing backups with a consistent landscape backup approach.

In contrast, note that this is currently not true for images created with Consistent Split. With Consistent Split, the database system has no knowledge of the backup, so with most systems, individual system recovery is not generally possible from such an image. Starting with an image created with Consistent Split on Oracle, for example, it is possible to do a complete single-system recovery, but it is not possible to do an incomplete database recovery.7

Figure 2 Sample Setup for Using Consistency Technology

Figure 2 gives an overview of a setup using consistency technology. The basic setup is the same for either method: The production landscape runs application processes that are constantly exchanging data . These processes write data to one or more storage systems. To create a consistent landscape image, an additional set of disks is available to hold the copy .

Depending on the approach, either the production volumes of the storage system(s) must be grouped together so they can be consistently split in a single operation or, with the Coordinated Suspend approach, you will create scripts and methods for suspending database write operations temporarily as the images are created by split-mirror .

This image can now be used to refresh a QA landscape or to restore the complete production landscape to a point of consistency . When using this image for landscape copy, any pending RFCs8 need to be processed to ensure data consistency in the copied landscape . To avoid having these RFCs go into the production landscape, careful precautions must be taken before starting the SAP systems on the landscape image!

For More Information
For more information on system landscape copy, see the corresponding Best Practices documents at http://service.sap.com/solutionmanagerbp.

Additional information on backup and restore concepts and strategies is available from the Best Practice “Backup and Restore for mySAP Business Suite” at http://service.sap.com/solutionmanagerbp and at http://service.sap.com/atg --> Backup and Restore.


1 The data is, from an application point of view, in a consistent state between the different systems.

2 Split-mirror copy traditionally refers to a single-system backup that temporarily halts WRITE operations in a controlled manner (SUSPEND/RESUME) and logs the status of transactions — as “complete” or “open” — in the database log. While the database is in SUSPEND mode, all volumes containing the database are copied on the storage level. See Siegfried Schmidt’s article in the January 2003 SAP Insider (www.SAPinsider.com).

3 By storage system, we mean here a dedicated computer with special-purpose disk storage management functions, specifically designed to consolidate the storage demands of multiple hosts.

4 RFC (Remote Function Call) tables.

5 For this particular use, note that — depending on the methods used to create the image — not all types of single-system recovery are possible from a consistent landscape image.

6 For other options offered by consistency technology, see the references at the end of the article.

7 If the image was created with Consistent Split and the database was not in "hot backup mode."

8 That is, those RFCs that were waiting to be processed when the split operation was executed


Jochen Wolter joined SAP in 1997 as a member of the Advanced Technology Group. There he was engaged in performance-tuning for SAP R/3 systems and Informix databases. Since 2000, his focus is on Backup & Restore concepts for SAP system landscapes. In addition to his work on the Federated Backup Project, he advises on Backup & Restore requirements with multi-system SAP landscapes.

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