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In this Document

Symptoms

Cause

Solution

Applies to:

Symptoms

IBM LTO - IBM LTO5, LTO6, LTO7, and LTO8 Drives Have Connectivity Issues and Possible CRC Errors with Brocade 16Gb FC Switches 

Cause

The 8Gb FC chipset used in the IBM LTO5, LTO6, LTO7, and LTO8 drives incorrectly send an IDLE Fillword to the FC Switch.  With Brocade 16Gb FC switches they have issues with this IDLE Fillword which will cause a loss of communication with the drive and possible CRC errors.

This can also cause drives to not be seen by the server after a server reboot.

Solution

There are 3 options that our customers have that will either be a workaround or a fix for this issue.

Option #1 - The customer can upgrade their Brocade 16Gb FC switch to FabricOS 8.0.1 or higher.  This firmware will automatically disabled the DFE feature on ports that have devices connected to them that have this 8Gb FC chipset.

Option #2 - The customer can upgrade their Brocade 16Gb FC switch to Fabric OS 7.1.2b or higher and then they will need to disable the DFE feature on the Brocade 16Gb FC switch.

To disable the DFE feature, follow the below steps:

1. Port needs to be set to fixed 8Gb port speed.  Run the "portcfgspeed <port number> 8" command on each port on the FC switch.
2. Enable NON-DFE on the FC switch.  Run the "portCfgNonDfe --enable <port number>" command on each port on the FC switch.

Note: For LTO tape drives the DFE feature should be disabled.  Since the above command is a negative command it needs to be enabled.  But this is actually disabled the DFE feature on that port.

Example Commands:
portCfgNonDfe --enable [slot/]port [-port]
portCfgNonDfe --disable [slot/]port [-port]
portCfgNonDfe --show [slot/]port [-port]
portCfgNonDfe --help

Usage: portCfgNonDfe Mode [Slot/]Port[-Range]
Mode:
--enable - Enable the portCfgNonDfe feature
--disable - Disable the portCfgNonDfe feature
--show - Show configuration for the non-DFE port
--help - Help command to display portCfgNonDfe Usage

If portCfgNonDfe is attempted on a non fixed 8G port, it will reject the cmd with this message:

Denied. Non-DFE mode is supported only in fixed 8G speed mode.
Please set port to fixed 8G mode via portCfgSpeed and then retry.

Option #3 - The customer can force all of the ports to a 4Gb port speed.  Run the "portcfgspeed <port number> 4" command on each port on the FC switch.

The DFE function is a calibration method added to Brocade Gen 5 switches. The Gen 4 (8gig) FC switch did not use this and there have been no
issues with them. The IDLE FIllword has a high frequency component that causes the DFE calibration to drift. This drift is detected as "noise" which
is detected as CRC errors on the switch receiver, although the data on the link is fine. The issue is highly intermittent and is very hard to reproduce.
It will show up as subtly as intermittent CRC errors (similar to a bad cable or SFP hardware) as the calibration drifts, or on the other extreme as a
completely dead link. You can restore the link by powering the drive or pulling the cable and plugging it back in.

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