Managing HP Serviceguard Extension for SAP for Linux, December 2013

4 SAP Netweaver cluster storage layout planning
Volume managers are tools that let you create units of disk storage known as storage groups.
Storage groups contain logical volumes for use on single systems and in high availability clusters.
In Serviceguard clusters, package control scripts activate the storage groups.
This chapter discusses disk layout for clustered SAP components and database components of
several vendors on a conception level. It is divided into two main sections:
• SAP Instance storage considerations
• Database Instance storage considerations
4.1 SAP Instance storage considerations
In general, it is important to stay as close as possible to the original layout intended by SAP. But,
certain cluster-specific considerations might suggest a slightly different approach. SGeSAP supports
various combinations of providing shared access to file systems in the cluster.
Table 3 Option descriptions
DescriptionOption
Optimized to provide maximum flexibility. Following the recommendations given below
allows for expansion of existing clusters without limitations caused by the cluster.
Another important design goal of SGeSAP option 1 is that a redesign of the storage
layout is not imperative when adding additional SAP components later on. Effective
change management is an important aspect for production environments. The disk
layout needs to be as flexible as possible to allow growth to be done by just adding
storage for newly added components. If the design is planned carefully at the
beginning, making changes to already existing file systems is not required.
1. SGeSAP NFS Cluster
Optimized to provide maximum simplicity. The option is only feasible for very simple
clusters. It needs to be foreseeable that the layout and configuration won't change
over time. It comes with the disadvantage of being locked into restricted configurations
with a single SAP System and idle standby nodes. HP recommends option 1 in case
of uncertainty about potential future layout changes.
2. SGeSAP NFS Idle Standby
Cluster
Each file system added to a system by SAP installation routines must be classified and a decision
has to be made:
• Whether the file system needs to be kept as a local copy on internal disks of each node of
the cluster (local).
• Whether the file system needs to be shared on a SAN storage device to allow failover and
exclusive activation (shared exclusive).
• Whether the file system to be allowed shared access to more than one node of the cluster at
the same time (shared NFS).
NOTE: SGeSAP packages and service monitors require SAP tools. Patching the SAP kernel
sometimes also patches SAP tools. Depending on what SAP changed, this might introduce additional
dependencies on shared libraries that weren't required before the patch. Depending on the shared
library path settings (LD_LIBRARY_PATH) of the root user, it may not be possible for SGeSAP to
execute the SAP tools after applying the patch. The introduced additional libraries are not found.
Creating local copies of the complete central executable directory prevents this issue.
The following sections details the different storage options.
4.1.1 Option 1: SGeSAP NFS cluster
With this storage setup, SGeSAP makes extensive use of exclusive volume group activation.
Concurrent shared access is provided via NFS services. Automounter and cross-mounting concepts
4.1 SAP Instance storage considerations 37