While Accessing your NSX-T Manager you might come across an issue where you might not be able to open the Web UI console to login.
While looking on the the VM Console you might see the above issue.
Failed to write entry, input/output error, Failed to rotate, Read-only file system.
All these error which you see on the above screen points out an issue with the Filesystem of the Appliance being in Read-only mode.
In order to come out of this situation you can simply Reset the Virtual Machine and it will boot the appliance again in Read/Write Mode.