Configuring Round Robin PSP When Using Dell EqualLogic Storage

 

Dell_EQLOver the last the month I have been involved in VMware vSphere upgrades or implementation projects for clients who are leveraging Dell EqualLogic arrays for their backend storage. If you have worked with the EqualLogic platform you can appreciate their ease of use and the great features sets that are included (Snapshots, Replication, VAAI support, etc). As these are iSCSI access only devices the trickier piece of implementing these arrays comes from the VMware vSphere side. With the advances in how the iSCSI stack works in each new release of VMware vSphere, the “proper” configuration for binding the iSCSI kernel ports has gotten easier. In vSphere 4.x this was accomplished via the command line, and now in vSphere 5.x this accomplished via the vSphere Client GUI interface. Both Dell and VMware have provided excellent resources on these proper procedures, outlined below:

Now this post is going to describe the process outlined in those documents, they all cover the basics of what needs to be implemented. However, the Dell documentation I believe needs to go one step further or at least show an “advanced” section around the configuration of the “Path Selection Policy” or “PSP”.  In Step 3 “Connect to a Volume on PS Series SAN” on page 32 of the “Configuring iSCSI Connectivity with VMware vSphere 5 and Dell EqualLogic PS Series Storage” it steps you through the process of changing the PSP from the VMware default of “Fixed” to “Round Robin”. At the end of the steps is this key note highlighted in bold:

NOTE – This needs to be done for every existing and new volume that you want the Round Policy to apply to

Seems like a lot manual work as well as something else to remember to do each time you create a new Volume/Datastore. If you are willing to roll up your sleeves and get dirty in the command line we can change the “default” from the VMware Fixed Path to VMware Round Robin per host and as Ron Popeil says, “Set it and forget it”.

As mentioned in the Dell documentation, in my test lab I have created and mounted a new Datastore from an EqualLogic unit, notice the “Path Selection” is configured to “Fixed (VMware)” by default and the “Storage Array Type” is listed as “VMW_SATP_EQL”:

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You can either SSH into your host or connect via the console. The examples I am using below I have connected to the ESXi host via SSH.

Step 1 – Using the esxcli storage nmp satp list command we will display the existing SATP’s and their default PSP’s they are configured to use:

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Step 2 – From the output in the command above you can see the default PSP for the EqualLogic arrays (VMW_SATP_EQL) is VMW_PSP_FIXED. To change this to the setting we are looking for, Round Robin (VMW_PSP_RR) we issue the esxcli storage nmp satp set –default-psp=VMW_PSP_RR –satp=VMW_SATP_EQL command:

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Step 3 – The output from the above command confirms it has been changed, but lets just double check using the command in Step1:

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As we can see highlighted the default PSP has been changed to VMW_PSP_RR

Step 4 – At this point all is left to do is put the host into maintenance mode and reboot for the changes to take affect. After the reboot I went back into the “Manage Paths” of my test Datastore to check the Path Selection Policy:

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Success! From this point forward any newly added Volumes/Datastores will be configured with the Round Robin PSP.

I will point out if you are licensed for VMware vSphere Enterprise or Enterprise Plus licensing you can leverage Dell’s Multipathing Extension Module, or MEM for short. With MEM installed all new volumes will be configured with Dell’s custom multipathing module, “Dell EqualLogic Path Selection”. Cormac Hogan (Blog / Twitter) at VMware has a write up from last year discussing the benefits of Dell’s MEM. You can read it HERE.

Comments

  1. Great post Jason. It might also be worth noting that if RR is going to be used, the user may want to change the default IOPS value from 1000 to 3 to provide better balancing between links. This is a Dell/EqualLogic Best Practice. The user can check the status of the datastore with:
    via esxcli storage nmp device list.
    It can be set with:
    esxcli storage nmp psp roundrobin deviceconfig set -d -I 3 -t iops

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