6.0.1

Figure 9‑1. Target Compared to LUN Representations
storage array
target
LUN LUN LUN
storage array
target target target
LUN LUN LUN
Three LUNs are available in each of these congurations. In the rst case, the host detects one target but that
target has three LUNs that can be used. Each of the LUNs represents individual storage volume. In the
second case, the host detects three dierent targets, each having one LUN.
Host-based iSCSI initiators establish connections to each target. Storage systems with a single target
containing multiple LUNs have trac to all the LUNs on a single connection. With a system that has three
targets with one LUN each, a host uses separate connections to the three LUNs. This information is useful
when you are trying to aggregate storage trac on multiple connections from the host with multiple iSCSI
HBAs, where trac for one target can be set to a particular HBA, while trac for another target can use a
dierent HBA.
iSCSI Storage System Types
ESXi supports dierent storage systems and arrays.
The types of storage that your host supports include active-active, active-passive, and ALUA-compliant.
Active-active storage
system
Allows access to the LUNs simultaneously through all the storage ports that
are available without signicant performance degradation. All the paths are
active at all times, unless a path fails.
Active-passive storage
system
A system in which one storage processor is actively providing access to a
given LUN. The other processors act as backup for the LUN and can be
actively providing access to other LUN I/O. I/O can be successfully sent only
to an active port for a given LUN. If access through the active storage port
fails, one of the passive storage processors can be activated by the servers
accessing it.
Asymmetrical storage
system
Supports Asymmetric Logical Unit Access (ALUA). ALUA-complaint
storage systems provide dierent levels of access per port. ALUA allows
hosts to determine the states of target ports and prioritize paths. The host
uses some of the active paths as primary while others as secondary.
Virtual port storage
system
Allows access to all available LUNs through a single virtual port. These are
active-active storage devices, but hide their multiple connections though a
single port. ESXi multipathing does not make multiple connections from a
specic port to the storage by default. Some storage vendors supply session
managers to establish and manage multiple connections to their storage.
These storage systems handle port failover and connection balancing
transparently. This is often referred to as transparent failover.
Discovery, Authentication, and Access Control
You can use several mechanisms to discover your storage and to limit access to it.
You must congure your host and the iSCSI storage system to support your storage access control policy.
vSphere Storage
66 VMware, Inc.