Veritas Storage Foundation 5.0 for Oracle RAC Configuration Guide Extracts for HP Serviceguard Storage Management Suite, Second Edition, May 2008

Investigating I/O Performance for SG Oracle RAC: Storage Mapping
Understanding Storage Mapping
Chapter 6
119
Understanding Storage Mapping
Access to mapping information is important since it allows for a detailed understanding
of the storage hierarchy in which files reside, information that is critical for effectively
evaluating I/O performance.
Mapping files to their underlying device is straightforward when datafiles are created
directly on a raw device. With the introduction of host-based volume managers and
sophisticated storage subsystems that provide RAID features, however, mapping files to
physical devices has become more difficult.
With the SG Oracle RAC Storage Mapping option, you can map datafiles to physical
devices. Veritas Storage Mapping relies on Veritas Mapping Service (VxMS), a library
that assists in the development of distributed SAN applications that must share
information about the physical location of files and volumes on a disk.
The Veritas Storage Mapping option supports Oracle’s set of storage APIs called Oracle
Mapping (“ORAMAP” for short) that lets Oracle determine the mapping information for
files and devices.
Oracle provides a set of dynamic performance views (v$ views) that shows the complete
mapping of a file to intermediate layers of logical volumes and physical devices. These
views enable you to locate the exact disk on which any specific block of a file resides. You
can use these mappings, along with device statistics, to evaluate I/O performance.
The Veritas Storage Mapping option supports a wide range of storage devices and allows
for “deep mapping” into EMC, Hitachi, and IBM Enterprise Storage Server (“Shark”)
arrays. Deep mapping information identifies the physical disks that comprise each LUN
and the hardware RAID information for the LUNs.
You can view storage mapping topology information and I/O statistics using the
following:
NOTE For SG Oracle RAC database, when you issue the commands, replace $ORACLE_SID with
$ORACLE_SID=instance_name and provide the instance name on which the instance is
running.
In addition, you can also use the Oracle Enterprise Manager GUI to display storage
mapping information after file mapping has occurred. Oracle Enterprise Manager does
not display I/O statistics information.
Table 6-1 View Storage and I/O Information Commands
vxstorage_stats This command displays the complete I/O topology mapping of
specific datafiles through intermediate layers like logical
volumes down to actual physical devices.
dbed_analyzer This command retrieves tablespace-to-physical disk mapping
information for all the datafiles in a specified database. It also
provides information about the amount of disk space being used
by a tablespace.