VMware ESXi and vSphere Cluster Management

iSCSI Initiators in VMware ESXi

Learn how software, dependent hardware, and independent hardware iSCSI initiators connect VMware ESXi hosts to targets, LUNs, and redundant storage paths.

An iSCSI initiator is the host-side component that establishes storage sessions with an iSCSI target. In VMware environments, an ESXi host uses an initiator to access block storage exported by an iSCSI SAN or NAS device.

The iSCSI target is the storage-side service or device. It presents logical storage units called LUNs to authorized initiators. The initiator requests access; the target supplies the storage.

How iSCSI communication works

iSCSI transports SCSI storage commands across TCP/IP networks. SCSI is a command set used to communicate with block-storage devices, while TCP/IP and Ethernet provide the network transport.

An ESXi host has an iSCSI initiator with an initiator identity, commonly an IQN.
The initiator uses a network path to contact one or more target portals.
The target authenticates and authorizes the initiator, if access controls are configured.
The target presents one or more LUNs.
ESXi discovers the LUN and its available paths, then can use it for storage operations such as a VMFS datastore.

Standard Ethernet cabling, switches, IP addresses, and TCP/IP networking can carry iSCSI traffic. The storage network may be dedicated or logically isolated with VLANs, depending on the design and requirements.

iSCSI names, portals, and LUNs

Successful discovery requires both correct identities and working network connectivity. An iSCSI name identifies an endpoint, while an IP address identifies where the endpoint can be reached.

IQN: An iSCSI Qualified Name is a standardized identifier for an initiator or target. An ESXi initiator IQN identifies the host to the storage system.
Initiator address: The IP address used by the initiator's storage network interface.
Target IQN: The identity of the target service that presents storage.
Target portal: A target network endpoint, normally represented by an IP address and TCP port. iSCSI commonly uses TCP port 3260.
LUN: A logical storage unit presented by the target to an authorized host.

Component	Role	Examples of identifiers or settings
ESXi host	Consumes block storage and runs or uses the initiator	Host identity, ESXi version
iSCSI initiator	Creates sessions to an iSCSI target	Initiator IQN, initiator network address
VMkernel adapter	Provides a logical ESXi interface for applicable storage traffic	IP address, VLAN, MTU
Physical NIC or adapter interface	Carries Ethernet traffic to the storage network	Uplink, switch port, link speed
iSCSI target	Presents block storage to authorized initiators	Target IQN, access rules
Target portal	Provides a reachable network endpoint for the target	Portal IP address and TCP port
LUN	Logical storage device made available to the initiator	LUN number, capacity, datastore use

Software iSCSI initiator in ESXi

The software iSCSI initiator is implemented in the ESXi VMkernel. It uses standard physical network adapters for iSCSI traffic, and the ESXi host CPU performs the iSCSI protocol processing.

Advantages

It provides iSCSI connectivity without purchasing a dedicated iSCSI adapter.
It can use ordinary Ethernet NICs that are supported by ESXi.
It fits environments where existing CPU capacity and network infrastructure meet the storage requirements.

Design considerations

CPU use: iSCSI processing consumes host CPU resources. The effect depends on traffic volume, workload, host capacity, and other features.
VMkernel networking: The storage VMkernel adapter, uplinks, VLANs, IP settings, and MTU must be configured correctly.
Storage-network design: Dedicated or isolated storage networks can reduce contention and simplify traffic control.
Multipathing: Multiple independent network and target paths can improve availability and may distribute I/O, subject to the storage design and supported path policies.

Example software-initiator layout

An ESXi host uses a VMkernel adapter on a dedicated storage VLAN. Standard Ethernet NICs carry traffic from that adapter to two target portal IP addresses. The software initiator establishes sessions to the portals, and the target presents a LUN that ESXi discovers and can use as a datastore.

Hardware iSCSI initiators in ESXi

A hardware iSCSI initiator is a dedicated Ethernet adapter that provides iSCSI connectivity and performs iSCSI processing in hardware. This is also called iSCSI offload: protocol work is moved from the ESXi host CPU to the adapter.

Hardware initiators are commonly divided into two categories:

Dependent hardware iSCSI adapters perform iSCSI processing but rely on ESXi VMkernel networking for connectivity and packet transport.
Independent hardware iSCSI adapters perform iSCSI processing and handle their own networking functions, configuration, and management interfaces.

Hardware offload may be considered when reduced host processing overhead, adapter-based storage processing, or a specific supported hardware design is important. The adapter, firmware, driver, and ESXi version must be compatible and supportable.

Dependent hardware iSCSI adapters

A dependent adapter contains hardware that performs iSCSI processing, but it does not operate as a completely separate storage network stack. It depends on ESXi VMkernel networking for network connectivity and packet transport.

Administrators therefore still configure the relevant VMkernel adapters, physical uplinks, VLANs, IP addressing, and other storage-network properties in ESXi. The adapter handles iSCSI protocol work, while the VMkernel-managed network path provides the connectivity.

Independent hardware iSCSI adapters

An independent hardware adapter handles both iSCSI processing and networking functions. It provides its own networking, configuration, and management interfaces and establishes the iSCSI path without relying on VMkernel networking for that storage traffic.

This creates a separate adapter-managed networking model. Administrators configure the adapter's network and management settings in addition to the general ESXi host network. VMkernel settings that control software or dependent-adapter traffic should not be assumed to control an independent adapter's iSCSI path.

Comparing ESXi iSCSI initiator types

Initiator type	Where iSCSI processing occurs	Network path dependency	Uses standard Ethernet NICs	VMkernel networking role	Separate adapter networking and management	Typical considerations
Software iSCSI initiator	ESXi host CPU and VMkernel	Uses the ESXi network path	Yes	Central to the storage path	No dedicated iSCSI adapter management	Low hardware cost; configure CPU, VMkernel networking, isolation, and multipathing
Dependent hardware iSCSI adapter	Dedicated adapter	Depends on VMkernel networking and its uplinks	Uses adapter hardware rather than an ordinary NIC alone	Required for connectivity and packet transport	Adapter-specific processing configuration may exist, but networking remains ESXi-dependent	Provides offload while retaining VMkernel network administration; verify compatibility
Independent hardware iSCSI adapter	Dedicated adapter	Uses the adapter's own network path	No separate standard-NIC-only path is required for its iSCSI traffic	Not used for the independent iSCSI network path	Yes; separate network and management configuration	Greater separation and offload; higher hardware, compatibility, and operational complexity

Choosing an initiator type

A standard network adapter is often sufficient when the ESXi host has suitable CPU capacity, the network is designed correctly, and the software initiator meets performance and support requirements. This can be a practical choice for small environments and many general-purpose deployments.

Specialized hardware may be considered when a workload has specific offload requirements, when an organization standardizes on supported adapter hardware, or when the operational design benefits from adapter-based processing. Hardware is not automatically faster or simpler; it introduces compatibility, firmware, cost, and management considerations.

Confirm support for the exact ESXi release, adapter model, firmware, and driver.
Evaluate storage throughput, latency, host CPU capacity, and expected growth.
Document who manages networking: ESXi VMkernel networking or the independent adapter's interfaces.
Compare the cost and complexity of dedicated hardware with the flexibility of standard NICs.
Design redundant paths rather than selecting an initiator type in isolation.

ESXi iSCSI network configuration

A storage network must be correctly configured before an initiator can discover a target. For software and dependent hardware initiators, VMkernel networking is central to this configuration.

Important network components

VMkernel adapters: Create or select interfaces intended for iSCSI traffic.
Physical uplinks: Associate suitable NICs with the virtual switch or distributed switch carrying the storage traffic.
VLANs: Use the correct storage VLAN when the network is logically segmented.
IP addressing: Assign addresses and routing appropriate for the initiator and target portals.
MTU: Keep MTU values consistent across the ESXi path, physical switches, and storage interfaces when using a non-default MTU.
Isolation: Consider dedicated links, VLANs, or other controls to limit contention and unwanted access.
Redundancy: Provide multiple network paths and target portals where the storage platform supports them.

Independent hardware adapters use their own networking interfaces for the iSCSI path. They still coexist with ESXi VMkernel networking for other host services, but their storage connectivity must be configured through the adapter's management model.

Software iSCSI configuration workflow

Enable the ESXi software iSCSI adapter.
Identify and record the initiator IQN.
Create or select a VMkernel adapter intended for iSCSI traffic.
Assign the correct IP address, VLAN, MTU, and physical uplink assignments.
Add target discovery information or static target details, including target IQNs and portal IP addresses.
Confirm initiator access permissions and authentication settings if authentication is used.
Rescan the storage adapter and verify discovered devices and paths.

Document before configuration:
Initiator IQN:       <ESXi initiator IQN>
Target IQN:          <storage target IQN>
Target portals:      <portal IP addresses and TCP port>
Storage VLAN:        <VLAN identifier>
VMkernel addresses:  <storage-network IP addresses>
MTU:                <consistent path MTU>
Redundant paths:     <network and target path plan>

Hardware iSCSI configuration workflow

Verify that the adapter, firmware, driver, and installed ESXi version are supported together.
Determine whether the adapter is dependent or independent.
For a dependent adapter, configure the required VMkernel networking path, uplinks, VLANs, IP settings, and MTU.
For an independent adapter, configure its own network and management interfaces as required by the adapter and storage design.
Configure target discovery, access permissions, and authentication where applicable.
Validate detected storage devices and all intended paths after rescanning.

Troubleshooting iSCSI initiator connectivity

The ESXi host cannot discover an iSCSI target

Confirm IP reachability between the initiator network interface and each target portal.
Verify VLAN membership, IP addressing, routing requirements, and MTU consistency.
Confirm that the intended software or hardware initiator is enabled and configured.
Verify target discovery details, target IQN values, and access permissions for the initiator IQN.
Rescan the storage adapter after correcting the configuration.

A software initiator cannot reach the storage network

Confirm that the intended VMkernel adapter is configured for iSCSI use.
Check virtual-switch or distributed-switch uplinks and the physical switch configuration.
Ensure that the VMkernel adapter has the correct storage-network IP address, VLAN, and MTU.

A dependent hardware adapter has no network connectivity

Verify VMkernel networking because the adapter depends on it.
Confirm the physical uplink association and storage VLAN connectivity.
Verify the adapter driver and ESXi compatibility.

An independent hardware adapter is not connecting

Verify the adapter's own network configuration and management settings.
Confirm target portal reachability from the adapter-managed interfaces.
Do not assume that VMkernel network settings control the independent adapter's iSCSI path.

Storage paths are missing or redundancy is incomplete

Confirm that every intended target portal is configured and reachable.
Validate that the target presents the LUN through each intended path.
Check physical network redundancy, switch configuration, and initiator-to-target access rules.
Rescan and review storage adapter path visibility.

Exam-relevant distinctions

Software initiator: VMkernel-based, uses standard NICs, and consumes ESXi host CPU for iSCSI processing.
Dependent hardware initiator: offloads iSCSI processing but still depends on VMkernel networking.
Independent hardware initiator: offloads iSCSI processing and provides its own networking and management interfaces.
IQN versus IP address: the IQN identifies an iSCSI endpoint; the IP address and TCP port identify a network endpoint used to reach it.
Initiator versus target: the initiator connects to storage; the target presents LUNs.
Multipathing: multiple storage paths improve resilience and may distribute I/O, but each path must be correctly configured and supported.

Summary

ESXi uses iSCSI initiators to connect hosts to block storage presented by iSCSI targets. The software initiator uses VMkernel networking, standard Ethernet NICs, and host CPU processing. A dependent hardware initiator moves iSCSI processing to an adapter but continues to rely on VMkernel networking. An independent hardware initiator also manages its own network path.

The right choice depends on supportability, cost, CPU and performance requirements, network design, redundancy, and operational complexity. Regardless of initiator type, correct IQNs, reachable target portals, valid access controls, consistent network settings, and verified storage paths are essential.

For related study, see iSCSI initiators in VMware ESXi.