Microsoft NTFS is one of the primary file systems of Windows. After installed it (reboot required), everything becomes fine. This is in fact a limited version of Paragon NTFS for use of Seagate Drive only. How can this happen? Finally, I found a solution on the Seagate official website. My Seagate Backup Plus is claimed to work on both Mac and Window.
Finally, I realised it is the NTFS problem. I have searched around for quite a while, and found out many others have similar problems after upgrading, such as this one one. I have upgraded my MBP to Yosemite the first day it was released, running into the trouble of mounting my Seagate Backup Plus External Hard Disk.
