H1B Check

Hi all,

I have a couple questions regards the H1B check. I came to USA with F1 Visa in 2001. In 2004, I went to Mexico to get F1 visa renew then went back to China for winter vaca. After graduated from University, I got a job, now is H1B. I am planning to go back to China to get a H1B renew. I had a feeling that there is good chance that I may get check, just based on 8 years that I havent be back home ( China). I am not sure how long this check process will take? Couple months or couple weeks? If I do get check, what documents I should prepared ? Thanks!