vsphere-esxi-vcenter-server-55-storage-guide

Chapter 23 Understanding Multipathing and FailoverFigure 23‐2. Host-Based Path FailoverhardwareiSCSIsoftwareiSCSIhost 1host 2softwareadapterHBA2HBA1NIC2NIC1IP networkSPiSCSI storageFailover with Hardware iSCSIWith hardware iSCSI, the host typically has two or more hardware iSCSI adapters available, from which thestorage system can be reached using one or more switches. Alternatively, the setup might include oneadapter and two storage processors so that the adapter can use a different path to reach the storage system.On the Host-Based Path Failover illustration, Host1 has two hardware iSCSI adapters, HBA1 and HBA2,that provide two physical paths to the storage system. Multipathing plug-ins on your host, whether theVMkernel NMP or any third-party MPPs, have access to the paths by default and can monitor health of eachphysical path. If, for example, HBA1 or the link between HBA1 and the network fails, the multipathingplug-ins can switch the path over to HBA2.Failover with Software iSCSIWith software iSCSI, as shown on Host 2 of the Host-Based Path Failover illustration, you can use multipleNICs that provide failover and load balancing capabilities for iSCSI connections between your host andstorage systems.For this setup, because multipathing plug-ins do not have direct access to physical NICs on your host, youfirst need to connect each physical NIC to a separate VMkernel port. You then associate all VMkernel portswith the software iSCSI initiator using a port binding technique. As a result, each VMkernel port connectedto a separate NIC becomes a different path that the iSCSI storage stack and its storage-aware multipathingplug-ins can use.For information on how to configure multipathing for software iSCSI, see “Setting Up iSCSI Network,” onpage 83.VMware, Inc. 217