1. A method of using a LUN (logical unit number) data type for storage allocation, the method comprising: specifying, by a file system of a computer, a LUN data type for a LUN from a plurality of LUN data types, the plurality of LUN data types including a database data type; receiving, by the file system, write data to be written into the LUN, wherein the write data has a LUN data type attribute; comparing, by the file system, the LUN data type attribute of the write data with the LUN data type of the LUN; if the LUN data type attribute of the write data matches the LUN data type of the LUN, then allocating, by the file system, at least some data blocks in the LUN for the write data, wherein a larger number of reserved data blocks are allocated in the LUN when the LUN data type is the database data type than are allocated when the LUN data type is another data type; and writing, by the file system, the write data into the LUN.