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Pure Technical Services

AVS and CBS Troubleshooting: iSCSI Multipathing

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Problem

Azure VMware Solution (AVS) and Pure CBS utilize the iSCSI block protocol to present a CBS-based datastore to AVS ESXi hosts.  iSCSI multipathing (MPIO) is a best practice that provides path redundancy, as well as performance benefits to those datastore connections between the two solutions. Utilizing iSCSI MPIO is a recommended best practice as it will help prevent an unplanned iSCSI datapath outage.  This article will focus on how and where to check to confirm that iSCSI is properly enabled and running as well as showing potential fixes to resolve any issues.

Impact

If MPIO is not implemented or experiences an issue, that can lead to a datastore potentially becoming unavailable, going offline or having performance impacts if an ESXi host or CBS controller VM goes down unexpectedly or for typical maintenance operations as there is no redundant path for the iSCSI connection to failover to.

Solution

Solution:  Confirm iSCSI MPIO has been enabled for AVS

ESXi iSCSI MPIO provides path resiliency and performance for the datapath connection between the AVS ESXi hosts and Pure Storage CBS iSCSI endpoints.  Supported AVS ESXi host types for this functionality are AV36, AV36p and AV52 SKUs.

The MPIO feature must be manually enabled by the customer and that action can be done so via the AVS portal.  This functionality can be gated by the earlyAccess flag.  To confirm that hte earlyAccess flag has been registered against your Azure subscription, run the following command from an Azure Cloud Shell prompt (make certain that the correct Azure Subscription has been set prior to running this command):

az feature show --namespace Microsoft.AVS --name earlyAccess --query properties.state 

To confirm MPIO itself is active, navigate to the following screen inside of the AVS Azure portal object:

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MPIO activation can also be confirmed by viewing each AVS ESXi host from the AVS vCenter GUI.  When iSCSI MPIO is properly enabled, two vmkernal adapters (vmk5 and vmk6) are added to each AVS ESXi host.  To confirm they are present, select an AVS ESXi host, navigate to ConfigureVMKernel adapters and ensure vmk5 and vmk6 are present.  Furthermore, the IP address for both vmkernel ports should be on the /24 CIDR block that was input during the MPIO enablement operation.

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Enabling MPIO is a recommended best practice and will potentially resolve single path connectivity between AVS ESXi hosts and Pure CBS.  Steps on how to enable iSCSI MPIO to be used with CBS can be found here.  Once MPIO is enabled via the AVS user providing a non-overlapping /24 network CIDR block the rest of the iSCSI MPIO enablement process is completely automated and typically takes anywhere from 15 - 30 minutes to complete.