VMW_PSP_MRU path ranking capabilities in ESXi 5.0
Article ID: 334611
Updated On:
Products
VMware vSphere ESXi
Issue/Introduction
In legacy ESXi releases, if an active I/O path to a target fails, VMW_PSP_MRU will randomly select one of the paths from a pool of active paths to the same target. It was not possible to predict what path VMW_PSP_MRU would select when the current I/O path failed.
In ESXi 5.0, VMW_PSP_MRU has path ranking capabilities that allows you to assign ranks to individual paths. VMW_PSP_MRU goes through the path group states in the following order: Active, Active_UO and Standby, and picks a path that has the highest rank for I/O.
As long as there are paths in the Active path group , the path is given preference over paths in the Active_UO and the Standby path groups, even if the path rank of a path in the Active group is less than that of a path in the Active_UO or the Standby path group.
By default, VMW_PSP_MRU sets all paths with rank zero. The default behavior of VMW_PSP_MRU is the same as legacy ESXi releases.
In ESXi 5.0, VMW_PSP_MRU has path ranking capabilities that allows you to assign ranks to individual paths. VMW_PSP_MRU goes through the path group states in the following order: Active, Active_UO and Standby, and picks a path that has the highest rank for I/O.
As long as there are paths in the Active path group , the path is given preference over paths in the Active_UO and the Standby path groups, even if the path rank of a path in the Active group is less than that of a path in the Active_UO or the Standby path group.
By default, VMW_PSP_MRU sets all paths with rank zero. The default behavior of VMW_PSP_MRU is the same as legacy ESXi releases.
Environment
VMware vSphere ESXi 5.0
Resolution
You can set path ranks using the following esxcli commands.
# esxcli storage nmp psp generic pathconfig get -p <vmhba pathname>
# esxcli storage nmp psp generic pathconfig set -p <vmhba Pathname>
-c rank=<Rank Number>
This function is currently limited to the CLI. You cannot set ranks to individual paths using the GUI.
Path Selection
VMW_PSP_MRU will go through the path group states in the following order: Active, Active_UO and Standby, and pick a path that has the highest rank. As a result, as long as there are paths in the Active path group, a path that has the highest rank in the Active path group is selected. If there are no paths in the Active path group, then the algorithm searches the Active_UO path group and the Standby path group in that order.
Path Failover
During failover, if there are no Active paths available, VMW_PSP_MRU attempts to activate a path that has the highest rank in ACTIVE_UO state. If no paths are available in the Active_UO state, VMW_PSP_MRU attemps to select a Standby path that has a highest rank for activation.
Path Failback
VMW_PSP_MRU fail-backs to a better ranked path or path with a better state when such a path becomes available. This is allowed because VMW_PSP_MRU will never fail-back to a path which requires activation, such as Active to Standby, or Active to Active_UO.
Array Support
VMW_PSP_MRU works for both Active/Active and Active/Passive arrays.
Known Issues
When paths are unclaimed by running esxcli claim rules, the path ranking information is lost. Run the command esxcfg-mpath -r to restore the path ranking information.
If you change the path ranking for a path, all paths are marked as non-current and the current path is marked as none if one of the following conditions is met:
# esxcli storage nmp psp generic pathconfig get -p <vmhba pathname>
# esxcli storage nmp psp generic pathconfig set -p <vmhba Pathname>
-c rank=<Rank Number>
This function is currently limited to the CLI. You cannot set ranks to individual paths using the GUI.
Path Selection
VMW_PSP_MRU will go through the path group states in the following order: Active, Active_UO and Standby, and pick a path that has the highest rank. As a result, as long as there are paths in the Active path group, a path that has the highest rank in the Active path group is selected. If there are no paths in the Active path group, then the algorithm searches the Active_UO path group and the Standby path group in that order.
Path Failover
During failover, if there are no Active paths available, VMW_PSP_MRU attempts to activate a path that has the highest rank in ACTIVE_UO state. If no paths are available in the Active_UO state, VMW_PSP_MRU attemps to select a Standby path that has a highest rank for activation.
Path Failback
VMW_PSP_MRU fail-backs to a better ranked path or path with a better state when such a path becomes available. This is allowed because VMW_PSP_MRU will never fail-back to a path which requires activation, such as Active to Standby, or Active to Active_UO.
Array Support
VMW_PSP_MRU works for both Active/Active and Active/Passive arrays.
Known Issues
When paths are unclaimed by running esxcli claim rules, the path ranking information is lost. Run the command esxcfg-mpath -r to restore the path ranking information.
If you change the path ranking for a path, all paths are marked as non-current and the current path is marked as none if one of the following conditions is met:
- You set the rank of the path you are changing higher than the rank of the current path.
- You reduce the current path's rank.
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