Multipathing policies in ESX/ESXi 4.x and ESXi 5.x

  • Most Recently Used (MRU)— Selects the first working path, discovered at system boot time. If this path becomes unavailable, the ESX/ESXi 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. ESX/ESXi does not return to the previous path when if, or when, it returns; it remains on the working path until it, for any reason, fails.Note: The preferred flag, while sometimes visible, is not applicable to the MRU pathing policy and can be disregard
  • Round Robin (RR)— 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 used in the Round Robin policy.
    • For Active/Active storage arrays, all paths will used in the Round Robin policy.

    Note: This policy is not currently supported for Logical Units that are part of a Microsoft Cluster Service (MSCS) virtual

  • Fixed (Fixed) — Uses the designated preferred path flag, if it has been configured. Otherwise, it uses the first working path discovered at system boot time. If the ESX/ESXi host cannot use the preferred path or it becomes unavailable, ESX/ESXi selects an alternative available path. The host automatically returns to the previously-defined preferred path as soon as it becomes available again. This is the default policy for LUNs presented from an Active/Active storage array.

    |Fixed path with Array Preference — The VMW_PSP_FIXED_AP policy was introduced in ESX/ESXi 4.1. It works for both Active/Active and Active/Passive storage arrays that support ALUA. This policy queries the storage array for the preferred path based on the arrays preference. If no preferred path is specified by the user, the storage array selects the preferred path based on specific criteria.

Notes:

  • These pathing policies apply to VMware’s Native Multipathing (NMP) Path Selection Plugins (PSP). Third party PSPs have their own restrictions.
  • Switching to Round Robin from MRU or Fixed is safe and supported for all arrays unless otherwise explicitly documented.

Warning: VMware does not recommend changing the LUN policy from Fixed to MRU, as the automatic selection of the pathing policy is based on the array that has been detected by the NMP PSP.

2180 Total Views 4 Views Today

Leave a Reply