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Multiple Access Paths to Host

Multi-pathing generally allows two or more data paths to be used simultaneously for read/write operations. This enhances performance by automatically and equally dispersing data access across all the available paths. Many storage and storage software vendors offer this kind of reliability.

We will examine some of the widely used solutions such as EMC’s Power Path, HP’s Secure Path, and Veritas’s Dynamic Multipathing solution.

Power Path (Dell / EMC)

EMC’s Power Path helps to improve the high availability of the data or I/O path and manages the heavy storage load. It automatically detects host failures and recovers the storage. Power Path is a host-based software that runs on Unix, Windows, and Linux servers. It can manage the protocols in both SCSI and fiber physical interconnects. Power Path creates a virtual ‘power device’ that provides failure resistance and a load-balanced path. Power devices are virtual objects that contain file systems or raw partitions. They are managed by a volume manager or host system. Each power device represents a LUN at the host level but remains available through multiple I/O paths. (See Fig 5.6)

Fig 5.6 Devices used in Power Path

Secure Path

HP's Secure Path is multipath, high availability software that manages and maintains continuous data access to HP storage systems. There is no single point of failure from the server to the storage. Secure Path is host-resident software that monitors the data paths between the server and the storage to increase the availability of the information. In the event a path failure is detected, Secure Path fails over the data path to an alternative path. When the original path becomes available, Secure Path can automatically fallback to the original path. Secure Path can also balance the workload among available paths to optimize system performance.

Dynamic Multi-Pathing

Dynamic Multipathing (DMP) is a feature of the Veritas Volume Manager. It offers greater reliability by providing a path failover mechanism. In the event a connection to a disk is lost, the system continues to access the critical data over the remaining sound connections to the disk. DMP also provides greater I/O throughput by balancing the I/O load uniformly across multiple I/O paths to the disk device.

MxMPIO

PolyServe Matrix Server supports multipath I/O in its driver stack. MxMPIO offers solid redundancy in the event of an HBA failure. Additionally, MxMPIO offers I/O load balancing by multiplexing I/O for varying LUNs between the different HBAs in the system. Bringing this feature to the Intel-based server-clustering arena makes commodity-based datacenter solutions one step closer to reality.


For more information, see the book Oracle 11g Grid and Real Application Clusters 30% off if you buy it directly from Rampant TechPress . 

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