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How To Troubleshoot Physical Connection Issue on SAN Switch

Introduction

In this post we will cover how to perform some basic troubleshooting on SAN switch connections that can lead to high enc_out/ crc_err /loss sig (for Brocade) or exceeded bit-error threshold (for cisco) and bad connections as well.

What Can Cause Connection Issues?

Here are some of the items that can lead to bad / faulty SAN Connections.

  • Faulty or bad cable.
  • Faulty or bad Gigabit Interface Converter (GBIC) or Small-Form Factor Pluggable (SFP).
  • GBIC or SFP speed doesn’t match with the port speed.
  • Short haul cable is used for long haul or long haul cable is used for short haul.
  • Momentary sync loss.
  • Loose cable connection at one or both ends.
  • Improper GBIC or SFP connection at one or both ends.
  • Fiber cable reversed polarity

Testing Bad / Faulty Connections

How to do physical connection test between SFP, cable and other side HBA?

  1. Identify the node and switch port involved in the communications failure.
  2. Verify that the switch port is administratively up (unblocked, no shut, or enabled).
  3. Move your SFP and fiber cable at the switch to any available unused port on the same switch.
  4. If the issue remains with the original port, then the switch is the issue. If not, then we know that the issue is either the SFP, fiber cabling, or node bus adapter.
  5. Move just the fiber cable back to your original port. Leave the SFPs you moved in step 2 still swapped between ports.
  6. If the issue returns to the original port, then the issue is either the fiber cabling or the node bus adapter. If the issue stays at the new port then the SFP is the problem.
  7. Once the SFP has been eliminated as the hardware problem, swapping cables is the next least intrusive troubleshooting test. With a known good working cable replace the original fiber cable between node and switch.
  8. If the issue remains, then the issue is at the node. Check out the HBA if a host, or else have the correct platforms group investigate their array’s fiber channel bus adapter in question (FA or SP).

Conclusion

In this post we covered a few ways to look at and possibly resolve connection issues with SAN, hope this is a starting point to help you resolve your issue.

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