iSCSI Architecture

iSCSI Components

Initiator (Host/Client):

• Software or hardware component that initiates iSCSI connections
• Identified by IQN (iSCSI Qualified Name)
• Example: iqn.1994-05.com.redhat:hostname

Target (Storage Array):

• Storage device that receives iSCSI connections
• Also identified by IQN
• Example: iqn.2010-06.com.storagevendor:array.12345abc

Portal:

• IP address and port combination for iSCSI access
• Default port: 3260
• Example: 10.100.1.10:3260

LUN (Logical Unit Number):

• Individual storage volume presented to initiator
• Appears as block device (e.g., /dev/sda)

Network Architecture Principles

1. Dedicated Storage Network

• Why: Isolates storage I/O from other traffic
• Benefit: Prevents bandwidth contention, enables QoS
• Implementation: Dedicated VLANs or physical networks

2. Redundant Paths

• Why: Eliminates single points of failure
• Benefit: High availability and load balancing
• Implementation: Multiple NICs and switches

3. Jumbo Frames (MTU 9000)

• Why: Reduces CPU overhead and improves throughput
• Benefit: Improved performance (verify with benchmarks in your environment)
• Requirement: Must be configured end-to-end

4. No Default Gateway

• Why: Prevents routing storage traffic
• Benefit: Keeps storage traffic local and secure
• Implementation: Static routes only if needed

Recommended Topologies

Topology 1: Basic Redundancy (2×2)

Pros:

• Simple configuration
• Good redundancy
• Adequate for most workloads

Cons:

• Limited bandwidth
• Single switch = single point of failure

Topology 2: High Availability (2×2 with Redundant Switches)

Pros:

• No single point of failure
• Switch maintenance without downtime
• Production-ready

Cons:

• Requires two switches
• More complex cabling

Topology 3: Maximum Performance (4×4)

Pros:

• Maximum bandwidth and redundancy
• Excellent for high-performance workloads
• Can sustain multiple failures

Cons:

• Requires more NICs and switch ports
• More complex configuration

VLAN Segmentation

Why use VLANs for iSCSI:

• Logical separation without dedicated switches
• Cost-effective redundancy
• Simplified management

Example configuration:

VLAN 100: Storage Network 1 (10.100.1.0/24)
VLAN 101: Storage Network 2 (10.100.2.0/24)

Host eth0.100 → Switch VLAN 100 → Storage Portal 1
Host eth0.101 → Switch VLAN 101 → Storage Portal 2

IP Addressing Scheme

Best practices:

• Use dedicated subnet for storage
• Static IP addresses (no DHCP)
• Consistent naming convention
• Document all assignments

Example:

Storage Network 1: 10.100.1.0/24
  - Host NICs: 10.100.1.11-10.100.1.99
  - Storage Portals: 10.100.1.10, 10.100.1.20

Storage Network 2: 10.100.2.0/24
  - Host NICs: 10.100.2.11-10.100.2.99
  - Storage Portals: 10.100.2.10, 10.100.2.20

Security Considerations

Network isolation:

• Dedicated VLANs or physical networks
• No routing to other networks
• Firewall rules to restrict access

Authentication:

• CHAP (Challenge-Handshake Authentication Protocol)
• Mutual CHAP for bidirectional authentication
• IQN-based access control on storage array

Encryption (optional):

• IPsec for data-in-transit encryption
• Performance impact: ~10-20%
• Required for compliance in some environments

Key points for RHEL:

• Use dedicated storage networks (VLANs or physical)
• Minimum 2×2 topology (2 NICs × 2 portals = 4 paths)
• Static IP addressing (no DHCP)
• No default gateway on storage interfaces
• MTU 9000 end-to-end