VMware vSphere default pathing policy

I am currently building a new vSphere farm at my company. This also includes the storage part, which can become a load of work:

  • First you have to fix up the physical cabling;
  • next, you have to setup up the zoning;
  • up next you have to present the virtual disks to the VMware hosts.

Last but not least you need to take care of pathing for your presented virtual disks. For our HP EVA SAN, vSphere defaults to the “Most Recently Used (VMware)” policy.
In the past we used to manually load balance using fixed paths. This was mainly because the round robin policy mechanism was still in an EXPERIMENTAL status.
The round robin policy offers great advantages over the default MRU policy:

  • The HP EVA offers ALUA (Asymmetrical Logical Unit Access). ALUA allows a LUN to be accessed via its primary path (via the owning Storage Processor) and via an asymmetrical path (via the not-owning Storage Processor) I/O to the not-owning Storage Processor or not-optimized path  comes with a performance penalty because the I/O has to be transmitted over the internal connection between the storage processors which does not have much bandwidth;
  • using ALUA in combination with Round Robin will load balance the I/O’s over the most optimized paths for that LUN;
  • the load is balanced between the two optimized paths rather then the most recently used path (as with the MRU policy).

Setting the pathing policy for each individual LUN can become quite a job. Good thing there is a way to set the default pathing policy for new discovered LUN’s using “esxcli”

esxcli nmp satp setdefaultpsp -–psp VMW_PSP_RR –-satp <Storage Array Type>

To figure out the storage array type for your virtual disk, right click a LUN and select “Manage Paths” (the screenshot highlights the Storage Array Type.

vmware_roundrobin

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One Response to “VMware vSphere default pathing policy”

  1. Nice post :-) Regards, S.

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