Ask for help from the great gods ~ ~ about the addition of servers ~ do you know any friends? ?

  mongodb, question

Everybody, help me out with an idea. Now the company uses MongoDB, version 2.6, one master, one slave and one arbitration node. Recently, when the traffic volume is large, the performance drops so fast that it wants to add another slave as a read server to improve the performance. However, the data volume is a bit large, about 2T. I wonder how this can be done without downtime.

@Amy_LoveBrother, have you finally solved this problem?