after create a new partition using 'fdisk /dev/sda', you must format it with a file system and mount it, or it can't use.

1. fdisk /dev/sda

2. partprobe /dev/sda

3. df -h

4. mkfs -t xfs /dev/sda3

5. mount /dev/sda3 /tmp

6. findmnt

7. umount /dev/sda3 /tmp