SAN multipathing verification steps

Overview

Multipathing (MPIO or vendor DSM) provides redundant fabrics. Half-configured path = silent single point of failure until reboot jiggles it.

Checks

• OS sees expected path count per LUN (usually 4 for dual fabric dual HBA).
• Active/Active vs ALUA state matches array doc—no dead paths showing Standby incorrectly forever.

After changes

FC zone edits, firmware bumps, HBA driver updates—run rescan and claimrule verification on Windows; multipath -ll on Linux.

Performance

Wrong load balance policy (RR vs LQD) hurts latency; storage vendor best practice paper is mandatory reading not optional.

Troubleshooting one path down

Check SFP errors, cable cleanliness, port masking on switch—log hours quickly; photo port labels.

Documentation

Visio fabric A/B colors consistent across clients—train eyes for faster triage.