iSCSI can be used to provide mobility for VMs and associated data onto and between VxRail environments. The figure below shows a VxRail environment that includes iSCSI storage in addition to the vSAN datastore.
Figure 63. Data mobility into and between VxRail environments
Data on the iSCSI storage is easily moved into the VxRail vSAN environment or between VxRail environments.
Existing iSCSI storage can also be used to provide additional capacity to the VxRail environment. However with the VxRail scale-up and scale-out configuration flexibility, external storage is typically not used to meet capacity requirements.
iSCSI provides block-level storage using the SCSI protocol over an IP network. SCSI uses a client-server, initiator-target model where initiators issue read/write operations to target devices, and targets either return the requested read data or persistently save write data. iSCSI in a VMware environment is standard functionality. A software adapter using the NIC on an ESXi host is configured as an initiator, and targets on an external storage system present LUNs to the initiators. The external LUNs could be used by ESXi as raw device mapping (RDM) devices, however usually, the use case is for VxRail to configure them as VMFS datastores. (Refer to vSphere documentation for more information: Using ESXi with iSCSI SAN.)
iSCSI configuration is performed using the vSphere web client. The steps involve creating a port group on the VDS, creating a VMkernel Network Adapter and associating it with the port group, and assigning an IP address. Then, from the vCenter Manage Storage Adapters view, the Add iSCSI Software Adapter dialog is used to create the software adapter. The last step is to bind the iSCSI software adapter with VMkernel adapter. Once this is complete, iSCSI targets and LUNs can be discovered and used to create new datastores and map them to the hosts in the cluster. (Refer to the VMware documentation for more details.)
iSCSI works best in a network environment that provides consistent and predictable performance, and a separate VLAN is usually implemented. iSCSI network requirements should be considered when planning the network requirements for VxRail environment to make sure connectivity to the external iSCSI storage system exists, and the additional network traffic will not impact other applications.