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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 SF 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 SF 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.