Understanding Storage Mapping

Access to mapping information allows for a detailed understanding of the storage hierarchy in which files reside. This information is critical to effectively evaluate I/O performance.

Mapping files to their underlying device is straightforward when datafiles exist directly on a raw device. With the introduction of host-based volume managers and sophisticated storage subsystems that provide RAID features, mapping files to physical devices is more difficult.

With the VERITAS Storage Mapping option, you can map datafiles to physical devices. VERITAS Storage Mapping relies on VERITAS Federated 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 the Oracle set of storage APIs called Oracle Mapping (ORAMAP) that lets Oracle determine the mapping information for files and devices.

Oracle provides a set of dynamic performance views (V$ views) that show 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. 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 arrays. Deep mapping information identifies the physical disks that comprise each LUN and the hardware RAID information for the LUNs.

View information on storage mapping topology and I/O statistics using:

• The vxstorage_stats command. This command displays the complete I/O topology mapping of a specific datafile from logical volumes down to actual physical devices.
• The VERITAS Storage Foundation for Oracle GUI. This GUI performs file mapping and displays information on storage mapping topology and I/O statistics.

The Oracle Enterprise Manager GUI also displays storage mapping information after file mapping takes place. Oracle Enterprise Manager does not display details on I/O statistics. Unlike the information displayed in the VERITAS Storage Foundation for Oracle GUI, the information displayed in Oracle Enterprise Manager may be "stale" or out of date.