Unable to add DataDomain DDBoost repository connected over Fibre Channel

When adding DataDomain as a backup repository using DDBoost over Fibre Channel, the following error is shown:

Failed to connect to 'DFC-'.
--tr:Unable to initialize Data Domain connection.
--tr:Failed to call DoRpc. CmdName: [DDBoostCheckConnection].
invalid argument. Err: 5008
Failed to connect to 'DFC-'.

If you can see DataDomain SCSI devices in the Device Manager on the proxy server please read following:

According to EMC Data Domain Boost Compatibility Guide (rev 19):

PowerPath v6.0 or greater on Windows, with the General Purpose Extension (GPX)
enabled.
PowerPath v5.7 or earlier on Windows, with the General Purpose Extension (GPX)

This means if you are using PowerPath v5.7 or earlier, GPX has to be disabled in order to work with DDboost.
PowerPath v6.0 or later should work with DDboost when GPX is enabled.

If you cannot see DataDomain SCSI devices in the Device Manager on the proxy server please read following:

According to EMC Data Domain Operating System Administration Guide:

Select one or more initiators. Optionally, replace the initiator name by entering a new one. An initiator is a backup client that connects to the system to read and write data using the FC (Fibre Channel) protocol. A specific initiator can support DD Boost over FC or VTL, but not both.
 

If you can see DataDomain SCSI device in the Device Manager on the proxy server please read following:

Make sure you are using PowerPath v6.0 or greater.

Alternatively, you can disable  PowerPath GPX or, if it doesn't help, uninstall PowerPath completely:

1 Uninstall PowerPath from Veeam backup proxy which DataDomain is connected to;
2. Reboot Veeam backup proxy;
3. Log into DataDomain management console;
4. Open DDBoost settings > Fibre Channel;
5. Change Server Name;
6. Disable Fibre Channel;
7. Re-enable Fibre Channel.

If you cannot see DataDomain SCSI device in the Device Manager on the proxy server please read following:

Please configure additional initiator explicitly for DD Boost or reconfigure existing one to work over DD Boost but not over VTL instead.