How Storage Helps Reduce the Total Cost of Ownership

February 18, 2003 by admin

Administrators need to make sure that all systems of a mySAP landscape have sufficient storage, and that added disks do not become hotspots that can impair business-critical I/O (Input/Output) throughput.
Monitoring and managing storage within each individual system of a mySAP landscape may become a challenge. With the ever-increasing need for continuous business availability, many SAP customers are finding they need storage solutions that go beyond additional disk space.
Happily, today’s state-of-the-art storage systems are more than just another container for business data. This article will introduce the key technology now available for enhanced management of storage in complex system environments — environments familiar to almost every SAP customer — as well as some of the business-critical features to look out for as administrators evaluate storage systems.

What Is a Storage System?

Storage systems go beyond the traditional approach of monitoring storage locally and managing it within each individual SAP system (i.e., the SAP Business Information Warehouse (SAP BW) solutions on one server, the SAP Customer Relationship Management (SAP CRM) solution on another). For the purposes of this discussion, a “storage system” is a dedicated computer with special-purpose disk storage management functions, specifically designed to consolidate the storage demands of multiple hosts. These functions enhance:

  • Reliability and Availability: All components of the storage systems are redundant, so that in case of a malfunction, the remaining component can take over the work. The data on the physical disks is RAID (Redundant Array of Independent Disks) protected. This means that the storage systems always keep redundant data in order to reconstruct the data in case of a failed disk.
  • Scalability: Should storage needs grow, the capacity of the storage systems can easily be expanded without impact on operation.
  • Performance: The storage system’s capability to stripe data across multiple physical disks — together with memory-cached I/O, and special-purpose CPUs for disk-to-cache as well as cache-to-host interfaces — offer business-critical high-I/O throughput.

The good news is that whether for large enterprises that spends a large part of its IT budget for storage or for smaller enterprises with more limited needs, today a variety of vendors offer this technology at reasonable prices. Nearly all storage manufacturers have started initiatives to provide tools capable of managing multi-manufacturer storage landscapes. And since these tools will protect a company’s storage investments, why wait to reap all the benefits that a storage system provides?

Key Features of Storage-Based Solutions for mySAP Landscapes

In collaboration with our partners from storage and database manufacturers, SAP makes every effort to offer solutions that optimize operation and infrastructure of mySAP landscapes.
Storage systems include fast copy functions available for copies within (local) and between (remote) storage systems. These copies are executed in the storage systems themselves without reducing a host’s CPU power. These capabilities, in combination with special database functions, allowed for the development of the split mirror solution methodology.

Split Mirror Solution

This is a key building block for storage solutions and provides a consistent copy of a database without any impact to operation. For this, the database systems offer functions that temporarily halt WRITE operations in a controlled manner (SUSPEND/RESUME) and log the status of transactions — as “complete” or “open” — in the database log.

NOTE

NOTE

While the database is in SUSPEND mode, all volumes that contain the database will be copied on the storage level. Of course, each implementation depends on the used database and storage system. However, the achieved copy (backup) can be used for a point-in-time recovery, and in combination with the recent DB-logs for a forward recovery.
Solutions based on the split mirror solution methodology provide:

  • Non-impact backup: Business operation is merely throttled, while the copy on the storage level is taken.
  • Fast recovery: Since the most recent backup is kept in the storage system, it can be used immediately for a recovery.
  • Landscape cloning: The point-in-time copy of a mySAP landscape can be used as an emergency system landscape, for read-only purposes or for testing system upgrades.

There are additional approaches that storage-based solutions can use to help further maximize your storage system: consistency groups, a concept that provides a split mirror solution without database participation, and remote copy capabilities — to provide a standby landscape for high data availability in case of a disaster.

Consistency Groups

Some storage systems, meanwhile, embrace the concept of “consistency groups” to suspend READ/WRITE operations. A consistency group consists of disks that are distributed over one or more storage systems. The idea behind this concept is to store the data for all the systems in a mySAP landscape in a consistency group, then use this group to create a consistent landscape copy while WRITE operations are suspended.
Unfortunately, database manufacturers do not currently recognize copies created in this way as “backups.” However, these copies can certainly be used to create a landscape clone. This new point-in-time copy of a mySAP landscape can then be used as an emergency system landscape for read-only purposes or for testing system upgrades.

Remote Copy Capabilities

Even a clone of a mySAP landscape may sometimes not fulfill the availability requirements. To be prepared for a major disaster — like the loss of the storage system or the entire computing center — the data of a mySAP landscape must be copied to a secondary storage system located either in the same or a remote computing center. This can be achieved by the storage system’s remote copy capability.

An Example of Storage Systems for a mySAP Landscape

SAP Landscape

SAP Landscape

Suppose a company has a mySAP landscape composed of three servers devoted to SAP R/3, SAP CRM, and SAP BW, and is looking to simplify its storage management processes. When adding a storage system to the landscape, the administrator could place primary and secondary storage systems on either a single computing center, or on two separate computing centers as in Figure 1. Choosing the latter setup provides maximum protection against both the loss of the primary storage system and the loss of the computing center it operates on.
Figure 1 depicts optimal storage layout, non-impact backup, standby landscape, and cloned landscape features in storage-based solutions.
In order to get the full I/O bandwidth for all systems of the mySAP landscape, the logical volumes are not only striped across the disks controlled by one disk adapter, but across all disk adapters.
All data changes on the primary system will be immediately copied via synchronous remote copy to the secondary system. The first mirror becomes the standby landscape copy.
A consistent backup of the landscape will be achieved by the split mirror solution. For this, the WRITE I/Os will be suspended on the primary side on the database level; in the secondary storage system, a second mirror will be created and copied to tape.
Here the administrator will find great benefits to availability: since the physical copy of the backup will be processed on the secondary storage system, the full I/O bandwidth of the primary system is available for the productive mySAP landscape.
After the backup, a cloned landscape can be started on the second mirror. Since this will modify the database images, they must be reloaded from tape in case of a recovery. To be able to provide a fast recovery nevertheless, a third mirror should be kept either on the primary or the secondary storage system.
Both the primary and the secondary hosts are connected by a switched fabric to the storage systems. The dotted lines between the primary hosts and the secondary storage system depict that the primary hosts can take over the data from first mirror in the secondary storage system should the primary hosts fail. In case the entire primary computing center is lost, the secondary hosts continue to work on the first mirror.

For More Information

Although most storage systems offer advanced data distribution strategies to avoid hotspots, SAP provides recommendations and best practices on how to lay out the databases of a mySAP landscape on a storage system. However, in case a customer does encounter trouble with I/O issues, SAP offers a storage optimization service. For more information, SAP customers can log on to
http://service.sap.com/stso.
Best practices and white papers regarding storage-based solutions are available from SAP or the storage manufacturers. For further information on these topics, SAP customers can refer to http://service.sap.com/atg.

Source: SAP Insider

Siegfried Schmidt

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