Embodiments relate to the field of storage technologies. The method is applied to a flash device whose first physical storage space stores a data block at a first security level and a data block at a second security level and whose second physical storage space stores a data block at a second security level. The method includes: receiving a data write request used to request to write target data, and obtaining a security level of the target data; and writing the target data into the first physical storage space if the security level of the target data is the first security level; or writing the target data into the second physical storage space or writing the target data into the second physical storage space and the first physical storage space if the security level of the target data is the second security level.