I've managed to resolve this by manually installing the MDM role from the /root/install directory.
An ESX server failed and took out the secondary MDM with it. I've since rebuilt it and redeployed another SVM using the deployment wizard. During the wizard I told it to add the SVM as a secondary MDM to replace the old one. The vsphere plugin then displayed the following message:  "Extending your ScaleIO system with another MDM requires that you update all SDCs in your system with the new MDM IP address. Run the drv_cfg utility on all SDCs with the --mod_mdm_ip option, and to make the change persistent, update the SDCs configuration file. For more information about the drv_cfg utility, see the user guide."  The user guide states that this utility isn't applicable on ESX environments, so I'm a tad confused as to why the plugin brings up this message. I've used the esxcli commands the user guide lists as an alternative to ensure all the SDCs list the correct MDM addresses. Everything looks in order; however, the new SVM is never configured as a secondary MDM as specified during the deployment wizard. I've checked via the cli (scli --query_cluster), to confirm this is the case. I've also tried to add the secondary via cli too:  scli --add_secondary_mdm --secondary_mdm_ip ,   I get the following error: Error: MDM failed command.  Status: Communication error  I can ping the IP's used in that command without issue. I get the feeling I'm missing something simple, but I'm unsure of where to check next? Any guidance appreciated!
Unable to add secondary MDM (VMware 6 / SIO 1.32)