10400424-002 04/2013
©2013 Overland Storage, Inc.
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Chapter 1
Path Manager Linux
Overview
PathManager is a software product for implementing path multiplexing between each server
and disk array unit in a system in which a Disk Array Subsystem is used. If a fault occurs on
a path, the used path can automatically be switched to another path. The concurrent use of
multiple paths can distribute the load to individual paths.
This chapter gives an overview of PathManager, and describes hardware and software
configurations and the other basic items and features of PathManager.
What Is PathManager?
Needless to say, to configure a SAN system, availability is important and the availability
greatly depends on the disk array units. Each disk array unit may become one of main faulty
locations in a system.
For this reason, many methods have been worked out and used to reduce the fault
occurrence rate for disk array units and smoothly recover from a fault. The methods include
RAID disk, Hot Spare, and replication.These solutions are effective only for media faults,
however. If a fault occurs in a host bus adapter, controller, or physical path (such as a fibre
channel cable or switch) between a server and a disk array unit, system operation cannot be
continued only with the redundancy of spindles. This is because there is no problem with
data in the disk array units, but the data cannot be accessed. Any disk array unit that is
proud of its strong position is helpless against a path fault.
Handling of Path Faults
PathManager provides an infrastructure to eliminate weaknesses lurking between a server
and a disk array unit in a system using path multiplexing.
If a fault occurs on a path and any access to the disk array unit is disabled during system
operation, PathManager detects the fault and switches the active path from the path on
which the fault occurs to another normal path to continue access to the disk array unit. The
path switching causes no I/O loss. The application can continue processing without
considering the occurrence of any path fault.
Load Distribution Function
PathManager has a load distribution function which uses the multiplexed paths to distribute
the load to individual paths. To make the most of the features, one static load distribution
mode and two dynamic load distribution modes, a total of three load distribution modes, are
available. You can use the load distribution function for more efficient access.
