Best Practices Guide for iSCSI on XCP-ng

Architecture Overview

Reference Architecture

A production-grade iSCSI deployment for XCP-ng consists of:

• XCP-ng Pool: 3+ hosts for high availability

  • Why: Minimum 3 hosts recommended for HA; allows maintenance without downtime

• Dedicated Storage Network: Isolated network infrastructure for storage traffic

  • Why: Prevents storage I/O contention with other traffic; ensures predictable performance; simplifies troubleshooting

• iSCSI Storage Array: Enterprise storage with multiple controllers

  • Why: Multiple controllers eliminate single point of failure; enable active-active multipath for performance and redundancy

• DM-Multipath Configuration: Multiple redundant paths for failover and load balancing

  • Why: Automatic failover on path failure; load distribution across all paths; no downtime during maintenance

Deployment Topology

VLAN-Tagged Multi-Subnet Architecture (Pure FlashArray Example)

Many enterprise storage arrays, including Pure FlashArray, use VLAN tagging to present iSCSI targets on multiple subnets from the same physical ports. This architecture requires special consideration for iSCSI discovery.

Key Concept: When VLAN tagging is enabled, each controller presents iSCSI targets on multiple VLANs. Discovery from any single IP only returns targets on that VLAN's subnet.

Example Pure FlashArray Configuration:

Discovery Behavior:

• Querying 10.10.3.10 returns: 10.10.3.10 (CT0) and 10.10.3.11 (CT1) - 2 targets

• Querying 10.10.4.10 returns: 10.10.4.10 (CT0) and 10.10.4.11 (CT1) - 2 targets

• To get all 4 targets: Query both subnets using comma-separated IPs

Configuration

GUI Configuration (Xen Orchestra)

In the XO iSCSI SR wizard, enter comma-separated IPs from each subnet:

Target: 10.10.3.10,10.10.4.10

CLI Configuration:

# Discovery from both subnets
iscsiadm -m discovery -t sendtargets -p 10.10.3.10:3260
iscsiadm -m discovery -t sendtargets -p 10.10.4.10:3260

# Create SR with multiple targets
xe sr-create name-label="Pure-iSCSI-SR" type=lvmoiscsi shared=true     device-config:target=10.10.3.10,10.10.4.10     device-config:targetIQN=iqn.2010-06.com.purestorage:flasharray.xxxx     device-config:SCSIid=3624a9370xxxxxxxxx

Result: 4 active paths (2 per controller, across 2 subnets)