Aix Mpio; Aix Subsystem Device Driver Path Control Module - IBM System Storage DS3500 Introduction And Implementation Manual

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The MPIO driver performs the following tasks:
Detects and claims the physical disk devices presented by the DS3500 Storage Systems
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 the
information about the behavior of storage subsystem devices in regard to:
– I/O routing information
– Conditions requiring a request to be retried, failed, failed over, or failed back
(for example, vendor-specific errors)
– Handling of miscellaneous functions, such as release/reservation commands
Multiple Device Specific Modules (DSMs) for various disk storage subsystems can be
installed in the same host server.
See 3.6.10, "Function of Auto-Logical Drive Transfer feature" on page 84 or more discussion
about multipathing and failover considerations.
For compatibility information, always see the current DS3500 interoperability matrix or the
readme file for your HBA driver. See the following Web site:
http://www.ibm.com/systems/support/storage/config/ssic/index.jsp

3.6.6 AIX MPIO

With Multiple Path I/O (MPIO), a device can be individually 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:
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 might 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.

3.6.7 AIX Subsystem Device Driver Path Control Module

The Subsystem Device Driver Path Control Module (SDDPCM) is a loadable path control
module for supported storage devices to supply path management functions and error
recovery algorithms. When the supported storage devices are configured as Multipath I/O
(MPIO) devices, SDDPCM is loaded as part of the AIX MPIO FCP (Fibre Channel Protocol)
device driver during the configuration. The AIX MPIO-capable device driver with the
supported storage devices SDDPCM module enhances the data availability and I/O load
balancing.
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IBM System Storage DS3500: Introduction and Implementation Guide
Draft Document for Review March 28, 2011 12:24 pm