Written by: Thomas Cornely, Senior Product Manager
This paper describes the Veritas Storage Foundation™ Dynamic Multi-pathing (DMP) feature that first appeared in DMP release 5.0. It was subsequently backported to the Solaris 4.1 code base in SxRT 4.1 MP2, the AIX 4.0 code base in AxRT 4.0 MP4 and the Linux 4.1 code base in LxRT 4.1 MP4. These three releases and up are collectively referred to as DMP Backport releases throughout these documents.
The paper provides a guide to understanding Dynamic Multi-pathing. For up-to-date information on features and coverage, readers should consult Symantec documentation and support sources.
Introduction - The Importance of Multiple Storage I/O Paths
The basic techniques for keeping business-critical computer applications and digital data available to users despite hardware and software failures are well-known:
- Applications. Applications can be protected against server failures by interconnecting two or more servers to form a cooperative cluster controlled by software that enables an application running on any of the servers to fail over and restart on another, should its own server fail.
- Data. Data can be preserved despite storage device failures by techniques such as mirroring identical copies on two or more disks and writing all updates to both simultaneously. Mirroring, sometimes called RAID-1, keeps data available if a disk fails, and also improves I/O performance by making two or more disks available to satisfy each application read request.
In enterprise data centers, there is another increasingly important link in the information access chain—the I/O path that connects servers with the data they process. The I/O path, represented in Figure 1, is a complex chain consisting of host bus adapter, cables, storage network switch, storage device adapter port, and, in disk arrays, a disk controller.
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