🔍 Deep Dive into VMware ESXi Path Selection Policies (PSPs)

In VMware ESXi, the Path Selection Policy (PSP) is a critical component of the Pluggable Storage Architecture (PSA) framework. PSPs determine how ESXi selects which physical path to use when accessing a storage device such as a SAN, iSCSI, or Fibre Channel array.

Choosing the right PSP directly impacts performance, reliability, and compliance with vendor recommendations. Let’s break down the options in detail.

🔑 PSP Options in ESXi

1️⃣ Fixed (VMW_PSP_FIXED)

• Behavior: Always uses a designated preferred path unless it fails.
• Advantages: Simple, predictable, and easy to troubleshoot.
• Limitations: Does not balance load across multiple paths.
• Best Fit: Active/Active arrays where one path is recommended or optimal.

2️⃣ Most Recently Used (MRU / VMW_PSP_MRU)

• Behavior: Uses the most recently active path. If that path fails, ESXi switches to another available path and sticks with it until failure again.
• Advantages: Works seamlessly with Active/Passive arrays, avoiding I/O to passive paths.
• Limitations: No load balancing; may not always use the most efficient path.
• Best Fit: Active/Passive arrays where only one path is active at a time.

3️⃣ Round Robin (RR / VMW_PSP_RR)

• Behavior: Rotates I/O requests across all available paths.
• Advantages: Provides load balancing and improved throughput for modern SANs.
• Limitations: Requires tuning (e.g., number of I/Os before switching paths) for optimal performance.
• Best Fit: Active/Active arrays where multiple paths can handle traffic simultaneously.

🛠️ Best Practices

• ✅ Round Robin → Use for modern SANs with multiple active paths to maximize throughput.
• ✅ MRU → Use for Active/Passive arrays to avoid sending I/O to passive paths.
• ✅ Fixed → Use if your storage vendor recommends a specific path for performance reasons.
• 📌 Always consult your storage vendor’s documentation — some arrays require a specific PSP for stability and support.

💡 Closing Thought

PSPs are not just technical settings — they are strategic choices that align your ESXi host with the architecture of your storage array. By selecting the right policy, you ensure optimal performance, reliability, and vendor compliance.

✨ “Infrastructure thrives when paths are chosen with clarity. The right policy turns every I/O into a step toward resilience.”