In fact, this method is try and error.
I'm now using Windows Server 2012, and, hmm, no need to say too much, just give the method.
1) Have two unused disks.
2) In "Disk Management", use "New Spanned Volume".
3) Use those two disks to create a volume. (Just default, default, next step, next step, finish)
4) Now we have a new volume which composed by two disks.
5) Use "Shrink Volume".
6) Enter a value which is bigger than the size of latter disk, for example, 20 GB + 20 GB, and the value may be 25 GB. Oh, the unit is MB.
7) Now we have a simple volume based on the former disk.
8) It doesn't matter to "Extend Volume" to re-allocate the un-allocated space to the simple volume, it will still be a simple volume. But if you select another disk, it will be spanned volume.
