My Cloud -USB Drive Backup

Hi,I have a My Cloud 3T. Connected to my home router used as a backup for all my photos. Recently it was running almost 95% of its capacity with 60G free only. I hooked out a newly bought portable 2T Transcend portable drive to the MY Cloud USB port at the rear. Use Dashboard USB Backup function created a job from NAS to USB backup one of my photos folder with synchronize option. I have the following questions:

  1. How to check the My Cloud sources folder size? I know its big and think it is almost 1.x T. Windows 10 cannot find the size nor dashboard.
  2. Speed is unknown. But I started the backup job 8 hours ago, seems that only 360G copied,as I saw my USB portable drive has 1.64T free ( I formatted the USB drive before doing this job ). Any other way I can backup my MY Cloud faster?

Thank you for your Help.