Dell Shared PowerEdge RAID Controller (PERC) 8 For Dell PowerEdge VRTX Systems User’s Guide

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Multipath and clustering setup in VMware

Multipath Settings—No recommended settings beyond the default settings

Cluster Settings:

In VMware, LUN contention can be an issue with large cluster deployments. Below are some guidelines and settings Dell recommends you use when configuring a cluster with shared storage:

  1. If possible have more than 1 LUN for data storage to reduce LUN contention and reservation conflicts.
  2. High numbers of VMs per LUN can also increase LUN contention. Due to varying workloads it is difficult to identify precise guidelines for VMs per LUN, but it is good practice not to exceed 64 virtual machines per LUN for proper optimization of your particular solution.
  3. The following values are recommended for Lun Queue Depth Throttling: 
                                              queuefullsamplesize:  32
                                          queuefullthresholdesize:  8
    Consult VMware documentation for more details on these settings and how to modify them.
    For more information, see VMware Knowledgebase article, “Controlling LUN queue depth throttling in VMware ESX/ESXi” (1008113).
  4. Setting the Maximum Outstanding Disk Requests for virtual machines:

    Dell recommends the following value for Maximum Outstanding Disk Requests From Competing Worlds: 
                                              NoOfOutstandingIOsWithCompetingWorlds:   128
    Consult VMware documentation for more details on this setting and how to modify it.
    For more information, see VMware Knowledgebase article, “Setting the Maximum Outstanding Disk Requests for virtual machines” (1268).
  5. DiskReservationThreshold:
    • VMWare defines this value as the “time window within which refcounted reservations on a device are permitted (in msec).” This setting can be used to increase the fairness of LUN reservations from multiple hosts. This setting can be found in the VSphere GUI.

      Dell recommends the following Disk Reservation Threshold:

      DiskReservationThreshold 1

  6. To help determine if you are getting reservation conflicts and to get additional logging to diagnose storage contention issues, the following log settings can be helpful: 
                                           ReservationBacktrace:   1 
                                          Scsi.LogScsiAborts:          1
                                          Scsi.LogCmdErrors:    1
    • NOTE: Some reservation conflicts are expected, and not all command errors signify a failure. Consult VMware documentation for additional information.

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