Data storage device and operating method thereof

A method for operating a data storage device includes providing a nonvolatile memory device including a page divided into a first half page and a second half page; dividing, when receiving data smaller than a size of a page, the data into first and second partial data; generating first and second valid data by adding metadata to the first and second partial data; generating first dummy data to be stored in the first half page together with the first valid data and second dummy data to be stored in the second half page together with the second valid data; storing the first valid data in the first half page and the second valid data in the second half page such that the first and second valid data are successive; and storing the first dummy data in an unused area of the first half page and the second dummy data in an unused area of the second half page.