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

vSphere StorageFigure 10‐1. Target Compared to LUN Representationstargettarget target targetLUN LUN LUNLUN LUN LUNstorage arraystorage arrayThree LUNs are available in each of these configurations. In the first case, the host detects one target but thattarget has three LUNs that can be used. Each of the LUNs represents individual storage volume. In thesecond case, the host detects three different targets, each having one LUN.Host-based iSCSI initiators establish connections to each target. Storage systems with a single targetcontaining multiple LUNs have traffic to all the LUNs on a single connection. With a system that has threetargets with one LUN each, a host uses separate connections to the three LUNs. This information is usefulwhen you are trying to aggregate storage traffic on multiple connections from the host with multiple iSCSIHBAs, where traffic for one target can be set to a particular HBA, while traffic for another target can use adifferent HBA.iSCSI Storage System TypesESXi supports different storage systems and arrays.The types of storage that your host supports include active-active, active-passive, and ALUA-compliant.Active-active storagesystemActive-passive storagesystemAsymmetrical storagesystemVirtual port storagesystemAllows access to the LUNs simultaneously through all the storage ports thatare available without significant performance degradation. All the paths areactive at all times, unless a path fails.A system in which one storage processor is actively providing access to agiven LUN. The other processors act as backup for the LUN and can beactively providing access to other LUN I/O. I/O can be successfully sent onlyto an active port for a given LUN. If access through the active storage portfails, one of the passive storage processors can be activated by the serversaccessing it.Supports Asymmetric Logical Unit Access (ALUA). ALUA-complaintstorage systems provide different levels of access per port. ALUA allowshosts to determine the states of target ports and prioritize paths. The hostuses some of the active paths as primary while others as secondary.Allows access to all available LUNs through a single virtual port. These areactive-active storage devices, but hide their multiple connections though asingle port. ESXi multipathing does not make multiple connections from aspecific port to the storage by default. Some storage vendors supply sessionmanagers to establish and manage multiple connections to their storage.These storage systems handle port failover and connection balancingtransparently. This is often referred to as transparent failover.Discovery, Authentication, and Access ControlYou can use several mechanisms to discover your storage and to limit access to it.You must configure your host and the iSCSI storage system to support your storage access control policy.72 VMware, Inc.