I recently added a new disk to my OMV 4.1.6. There were some problems getting the disk fully recognized such that it appeared in the various drop down lists, but that was resolved by making a manual fix in its mtent section in config.xml. This might be a bug and I will confirm in another thread when I attempt to add another new disk soon.
In the meantime there is misbehavior with this disk in the OMV Diagnostics | System Information | Performance Statistics | Disk usage. The graph does not appear and all that is shown is the series of faces with frowns.
However, in OMV Diagnostics | System Information | Performance Statistics | Disk I/O the disk's traffic graph is there and appears correct.
I have used the omv-firstaid Check RRD database tool in the shell. All this shows is numerous files with timestamps in the future, so I delete those. But running the tool again shows the same files again with future timestamps.