One morning, all permissions on my 4TB drive were wiped out. All files were inaccessable. I restored permissions via GUI by setting at drive leval and having permissions propergate down. This worked but took upwards of 2 days to complete

Questions: 1 How could this have happened other than deliberately
2. Should the restore take this long or am I doing something wrong
3. What might be a quicker method to restore a drive this size

Thanks