Oracle ASM and Multipathing

Multipathing solutions provide failover by using redundant physical path components. These components include adapters, cables, and switches that reside between the server and the storage subsystem. If one or more of these components fails, then applications can still access their data, eliminating a single point of failure with the Storage Area Network (SAN), Host Bus Adapter, interface cable, or host port on a multiported storage array.

Multipathing is a software technology implemented at the operating system device driver level. Multipathing creates a pseudo device to facilitate the sharing and balancing of I/O operations across all of the available I/O paths. Multipathing also improves system performance by distributing the I/O load across all available paths, providing a higher level of data availability through automatic failover and failback.

Although Oracle ASM is not designed with multipathing functionality, Oracle ASM does operate with multipathing technologies. Multipathing technologies are available from many sources. Storage vendors offer multipathing products to support their specific storage products, while software vendors usually develop multipathing products to support several server platforms and storage products.

With Oracle ASM, you can ensure the discovery of a multipath disk by setting the value of the ASM_DISKSTRING initialization parameter to a pattern that matches the pseudo devices that represents the multipath disk. When I/O is sent to the pseudo device, the multipath driver intercepts it and provides load balancing to the underlying subpaths.

If Oracle ASM discovers multiple paths to the same disk device, Oracle ASM then raises an error. Because a single disk can appear multiple times in a multipath configuration, you must configure Oracle ASM to discover only the multipath disk.

For information about disk discovery, see "Oracle ASM Disk Discovery ".