You notice the hard drive has very little free space, and OneDrive for Business has stopped synchronizing.
Also you notice that the folder where the OfficeFileCache is now 2 or more times the size of the synced OneDrive and Sharepoint team sites. For example, the library is 50 GB and the Officefilecache folder is 100 GB.
Though the PST file extension is not on the list of restricted file types, it is strongly suggested that you do not store them in OneDrive for Business if they are still connected to Outlook, as it will continuously add information to the cache.
This added information in a duplicate file will cause the large Office File Cache issue. This is likely to lead to problems synchronizing files in OneDrive for Business client.
A PST (Personal Storage) file or files that are in use by Outlook, such as the Archive or personal PST, are stored in a synced folder by the OneDrive for Business client application. This causes the OfficeFileCache folder to be larger than the original synced location. When Outlook opens the PST file, it creates a corresponding temp file in the same location. For example, Outlook opens archive.pst, it will create a file ~archive.pst.
Written by: Scotland Welch