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The types of storage that your host supports include active-active, active-passive, and ALUA-compliant.
Active-active storage
system
Supports access to the LUNs simultaneously through all the storage ports
that are available without significant performance degradation. All the paths
are always active, 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 a 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-compliant storage
systems provide different levels of access per port. With ALUA, hosts can
determine the states of target ports and prioritize paths. The host uses
some of the active paths as primary and others as secondary.
Virtual port storage
system
Supports access to all available LUNs through a single virtual port. Virtual
port storage systems are active-active storage devices, but hide their
multiple connections though a single port. ESXi multipathing does not make
multiple connections from a specific 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
failovers and connection balancing transparently. This capability is often
called transparent failover.
Discovery, Authentication, and Access Control
You 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.
Discovery
A discovery session is part of the iSCSI protocol. It returns the set of targets you can access on an iSCSI
storage system. The two types of discovery available on ESXi are dynamic and static. Dynamic discovery
obtains a list of accessible targets from the iSCSI storage system. Static discovery can access only a
particular target by target name and address.
For more information, see Configuring Discovery Addresses for iSCSI Adapters.
Authentication
iSCSI storage systems authenticate an initiator by a name and key pair. ESXi supports the CHAP
authentication protocol. To use CHAP authentication, the ESXi host and the iSCSI storage system must
have CHAP enabled and have common credentials.
For information on enabling CHAP, see Configuring CHAP Parameters for iSCSI Adapters.
vSphere Storage
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