Hidden File in CASLib Path

[Eddie305]

Dear colleagues,

Although my question is related to an old Viya3 system on Windows, but I would like to understand more the nature of the file.

I noticed that there are a large number of hidden files _B__T_F*.sashdat in the CASLib data path. I can't recognise the file name and its nature. Does anyone know what it is? As the last modified date of the files is over a year before, can I delete them safely? 

Any special handling we need to take care of if we want to migrate to Viya4?