New Volume was Not Showing
I found there's no volume shown in web GUI of FreeNAS in Chrome like below.

FreeNAS New Volume Not Show in Chrome
The sidebar shows that the new volume does exist. But I can't see any list in the content section.
Workaround
I simply switch to another browser, for example, Internet Explore (IE) to access the web GUI of FreeNAS.

FreeNAS New Volume Show in IE
It seems a display problem between browsers.