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. 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: I/O algorithms Health check mode and interval 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. Chapter 1. General enhancements  23 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. 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. 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: