136 IBM Midrange System Storage Hardware Guide
The MPIO driver performs the following tasks:
Detects and claims the physical disk devices presented by the DS5000 storage
subsystems based on vendor/product ID strings and manages the logical paths to the
physical devices.
Presents a single instance of each LUN to the rest of the Windows operating system.
Provides an optional interface through WMI for use by user-mode applications.
Relies on the vendor’s (IBM) customized Device Specific Module (DSM) for information
about the behavior of storage subsystem devices for the following items:
– I/O routing information
– Conditions requiring a request to be retried, failed, failed over, or failed back (for
example, vendor-unique errors)
– Handles miscellaneous functions, such as release/reservation commands
Multiple Device Specific Modules (DSMs) for different disk storage subsystems can be
installed in the same host server.
See 4.4.10, “Auto Logical Drive Transfer (ADT) feature” on page 138 for more details about
multipathing and failover considerations.
For compatibility information, always see the current DS5000 interoperability matrix or the
readme file for your HBA driver. The matrix can be found at:
http://www-01.ibm.com/systems/support/storage/config/ssic/index.jsp
4.4.6 AIX MPIO
With Multiple Path I/O (MPIO), a device can be uniquely detected through one or more
physical connections, or paths. A path-control module (PCM) provides the path management
functions.
An MPIO-capable device driver can control more than one type of target device. A PCM can
support one or more specific devices. Therefore, one device driver can be interfaced to
multiple PCMs that control the I/O across the paths to each of the target devices.
The AIX PCM has a health-check capability that can be used to do the following actions:
Check the paths and determine which paths are currently usable for sending I/O.
Enable a path that was previously marked failed because of a temporary path fault (for
example, when a cable to a device was removed and then reconnected).
Check currently unused paths that will be used if a failover occurred (for example, when
the algorithm attribute value is failover, the health check can test the alternate paths).
MPIO is part of the AIX operating system and does not need to be installed separately. You
can find more information about MPIO in IBM Midrange System Storage Implementation and
Best Practices Guide, SG24-6363.
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