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Multipathing policies in ESXi 5.x and ESXi/ESX 4.x (1011340)
Note: These are referred to as Path Selection Plug-ins (PSP), and are also called Path Selection Policies.
- Most Recently Used (MRU): The VMW_PSP_MRU policy selects the first working path, discovered at system boot time. If this path becomes unavailable, the ESXi/ESX host switches to an alternative path and continues to use the new path while it is available. This is the default policy for Logical Unit Numbers (LUNs) presented from an Active/Passive array. ESXi/ESX does not return to the previous path if, or when, it returns; it remains on the working path until it, for any reason, fails.
preferredflag, while sometimes visible, is not applicable to the MRU pathing policy and can be disregarded.
- Fixed (Fixed): The
VMW_PSP_FIXEDpolicy uses the designated
preferredpath flag, if it is configured. Otherwise, it uses the first working path discovered at system boot time. If the ESXi/ESX host cannot use the
preferredpath or it becomes unavailable, the ESXi/ESX host selects an alternative available path. The host automatically returns to the previously defined
preferredpath as soon as it becomes available again. This is the default policy for LUNs presented from an Active/Active storage array.
- Round Robin (RR): The VMW_PSP_RR policy uses an automatic path selection, rotating through all available paths, enabling the distribution of load across the configured paths.
- For Active/Passive storage arrays, only the paths to the active controller will be used in the Round Robin policy.
- For Active/Active storage arrays, all paths will be used in the Round Robin policy.
Note: For logical units associated with Microsoft Cluster Service (MSCS) and Microsoft Failover Clustering virtual machines, the Round Robin pathing policy is supported only on ESXi 5.5 and later.
- Fixed path with Array Preference: The
VMW_PSP_FIXED_APpolicy was introduced in ESXi/ESX 4.1. It works for both Active/Active and Active/Passive storage arrays that support Asymmetric Logical Unit Access (ALUA). This policy queries the storage array for the preferred path based on the array's preference. If no preferred path is specified by the user, the storage array selects the preferred path based on specific criteria.
VMW_PSP_FIXED_APpolicy is removed from ESXi 5.0. For ALUA arrays in ESXi 5.0, the
MRUPath Selection Policy (PSP) is normally selected but some storage arrays need to use
Fixed. To check which PSP is recommended for your storage array, see the Storage/SAN section in the VMware Compatibility Guide or contact your storage vendor.
- These pathing policies apply to VMware's Native Multipathing (NMP) Path Selection Plug-ins (PSP). Third-party PSPs have their own restrictions.
- Round Robin is not supported on all storage arrays. Please check with your array documentation or storage vendor to verify that Round Robin is supported and/or recommended for your array and configuration. Switching to an unsupported or undesirable pathing policy can result in connectivity issues to the LUNs (in a worst-case scenario, this can cause an outage).
Warning: VMware does not recommend changing the LUN policy from
MRU, as the automatic selection of the pathing policy is based on the array that is detected by the NMP PSP.
- The Round Robin (RR) multipathing policies have configurable options that can be modified on the command line. Some of these options include:
- Number of bytes to send along one path for this device before the PSP switches to the next path.
- Number of I/O operations to send along one path for this device before the PSP switches to the next path.
esxcli storage nmp psp roundrobinin the vSphere Command-Line Interface Installation and Reference Guide for the appropriate version of your VMware product.
- If the storage device is configured for Asymmetric Logical Unit Access (ALUA), Round Robin by default will use only the active optimized paths. Note: This behavior can be changed, but not recommended as it may result in performance degradation. For more information, see Managing NMP with esxcli storage nmp section of the vSphere Command-Line Interface Documentation guide.
- To change a LUN to use the Round Robin path policy, see Changing a LUN to use a different Path Selection Policy (PSP) (1036189).
- To change newly provisioned LUNs to use Round Robin by default, see Changing the default pathing policy for new/existing LUNs (1017760).
- For more information, search for Multipathing Considerations and PSP in the vSphere 5 Documentation Center; for 5.5 vSphere 5.5 Documentation Center
- For translated versions of this article, see:
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