AIXPCM benefits from being integrated into the OS, which removes the need for separate maintenance activities that are related to updating the PCM. By being integrated, your regular OS maintenance results in the PCM being updated, which simplifies the management of your AIX environments. 

When using the default AIXPCM, you can set two types of attributes: device attributes and path attributes. These attributes can be modified to suit your system configuration based on your individual requirements, and can be defined on a per device basis if required. 

## I/O algorithms 

One attribute that can be changed is the algorithm  attribute. It determines the way I/O is distributed across the paths that are available for a device. There are three different algorithms for I/O distribution: 

fail_over In this mode, I/O is sent over one enabled path, and another path is used only if this path fails. The initial path that is selected is the one with the highest priority (the lowest path priority value). If this path fails, the next highest priority path is selected for I/O operations. This is the default algorithm for iSCSI and FC devices. 

round_robin In this mode, I/O is distributed across multiple enabled paths. For any device that has preferred and non-preferred paths or active and passive paths, only a subset of paths is used. Paths that have a higher path priority receive a larger share of I/O operations in this mode. 

shortest_queue In this mode, an I/O path is distributed across multiple enabled paths. For any device that has preferred and non-preferred paths or active and passive paths, only a subset of paths is used. In this mode, path priority is ignored, and paths are selected based on the number of pending I/O operations only. The path with the lowest number of pending I/O operations is selected for I/O. 

## Health check mode and interval 

Another key device attribute is the hcheck_mode  attribute. This attribute determines which paths are probed when the health check capability is used. Health checking is only performed on devices that have a state of open . A device that is not in use does not have its paths health checked. Health checking is also not performed on any disabled or missing paths. There are three health check modes: 

Enabled In this mode, the healthcheck  command is sent to all paths that are enabled for the device, which includes paths that failed. 

Failed In this mode, the healthcheck  command is sent to all paths that are in a failed state for the device. 

Nonactive In this mode, the healthcheck  command is sent to all paths that do not have any active I/O, which includes paths that are in enabled and failed states. This is the default health check mode that is configured on AIX. 

Along with hcheck_mode , you can also configure how often the health check is performed by configuring the hcheck_interval  value. This attribute can be set to any value 0 - 3600, and it represents the time in seconds between polling. If a value of 0  is specified, it indicates that health checking should be disabled on the device. The default value for hcheck_interval  is set to perform health checking every 60 seconds. 

