The Azure VMware Solution (AVS) ESXi hosts connect to Everpure Cloud Dedicated via the iSCSI block protocol. In order for these two endpoints to communicate with one another, one (but ideally multiple) iSCSI paths must exist between each AVS ESXi host iSCSI software adapter inside of the designated AVS Cluster and the Everpure Cloud Dedicated controller VMs iSCSI endpoints. Initializing this connectivity is covered in-depth at the following Azure Run Command Storage Management Overview. If the implementation guide has not been followed previously, it is strongly recommended to review the entire Implementation Guide as many of the potential issues shown below can be avoided via a proper environment setup.
Once iSCSI connectivity is established, it is possible that the iSCSI paths between the AVS ESXi hosts and Everpure Cloud Dedicated can go offline for a myriad of reasons. This topic will cover common ways these paths can go down, common methods to check path status as well as ways to remediate and restore inactive iSCSI paths to an active state.
To start, we will show and explain the different ways in which a loss of iSCSI connectivity can impact a running AVS and Everpure Cloud Dedicated deployment.
Problem 1: A VMFS datastore inaccessible to the entire AVS Cluster
From the Azure VMware Solution vCenter console, a Everpure Cloud Dedicated-backed VMFS datastore shows as 'inaccessible' from within the GUI, similar to as depicted in the below screenshot.
In this scenario, the datastore cannot be accessed by the AVS vCenter cluster and all virtual machines that reside on the VMFS volume may also show up as inaccessible or otherwise go offline.
For this example from the Everpure Cloud Dedicated GUI, we can see that the VMFS volume has no AVS host group connectivity:
Problem 2: VMFS datastore is inaccessible to one or more (but not all) AVS ESXi hosts in a cluster
In this scenario, a VMFS datstore is available to only a few individual AVS ESXi hosts within a cluster, but is not available to all hosts. The below screenshots show two hosts in a cluster: one with VMFS datastore connectivity and one without.
From the Everpure Cloud Dedicated GUI, we can see the the host not showing the VMFS datastore in the vCenter GUI also has no iSCSI paths shown from the Everpure Cloud Dedicated GUI.
Problem 3: Individual iSCSI paths down between AVS and Everpure Cloud Dedicated but VMFS datastore remains accessible
This problem may not result in an outage but should still be resolved in order to have both the path resiliency as well as path performance afforded by having multiple available paths between AVS and Everpure Cloud Dedicated. Single iSCSI path status can be easily check from Everpure Cloud Dedicated.
From the Everpure Cloud Dedicated GUI, we can see that the AVS host shown has 'Single Controller' connectivity. This means that a single iSCSI path is connected from the Everpure Cloud Dedicated CT0 controller, but not from CT1.