FRESULT f_mkfs (
  const TCHAR* path,   /* [IN] Logical drive number */
  const MKFS_PARM* opt,/* [IN] Format options */
  void* work,          /* [-]  Working buffer */
  UINT len             /* [IN] Size of working buffer */
);

Description

The FAT sub-type, FAT12/FAT16/FAT32, of FAT volume except exFAT is determined by only number of clusters on the volume and nothing else, according to the FAT specification issued by Microsoft. Thus the FAT sub-type of created volume depends on the volume size and the cluster size. In case of the combination of FAT type and cluter size specified by argument is not valid for the volume size, the function will fail with FR_MKFS_ABORTED.

The allocation unit, also known as cluster, is a unit of disk space allocation for files. When the size of allocation unit is 32768 bytes, a file with 100 bytes in size occupies 32768 bytes of disk space. The space efficiency of disk usage gets worse as increasing size of allocation unit, but, on the other hand, the read/write performance increases. Therefore the size of allocation unit is a trade-off between space efficiency and performance. For the large volumes in GB order, 32768 bytes or larger, automatically selected by default, is recommended for most case unless extremely many small files are created in the volume.

When the logical drive to be formatted is associated with a physical drive (FF_MULTI_PARTITION == 0 or VolToPart[].pt == 0) and FM_SFD flag is not specified, a partition occupies entire drive space is created and then the FAT volume is created in the partition. When FM_SFD flag is specified, the FAT volume is created without any disk partitioning.

When the logical drive to be formatted is associated with a specific partition by multiple partition feature (FF_MULTI_PARTITION == 1 and VolToPart[].pt > 0), the FAT volume is created in the partition of the physical drive specified by volume mapping table and FM_SFD flag is ignored. The hosting physical drive needs to be partitioned with f_fdisk function or any partitioning tool prior to create the FAT volume with this function. If the partition is not exist, the function aborts with FR_MKFS_ABORTED.

There are three standard disk partitioning formats, MBR, GPT and SFD. The MBR format, also known as FDISK format, is usually used for harddisk, memory card and U disk. It can divide a physical drive into one or more partitions with a partition table. The GPT, GUID Partition Table, is a newly defined patitioning format for large storage devices. FatFs suppors the GPT only when 64-bit LBA is enabled. The SFD, Super-Floppy Disk, is non-partitioned disk format. The FAT volume is located at LBA 0 and occupies the entire physical drive without any disk partitioning. It is usually used for floppy disk, optical disk and most super-floppy media. Some combination of systems and media support only either partitioned format or non-partitioned format and the other is not supported.

Some systems manage the partitions in the on-board storage in non-standard format. The partitions are mapped as physical drives identified by pdrv in disk_* functions. For such systems, SFD format is suitable to create the FAT volume in the partition.

/* Format default drive and create a file */
int main (void)
{
    FATFS fs;           /* Filesystem object */
    FIL fil;            /* File object */
    FRESULT res;        /* API result code */
    UINT bw;            /* Bytes written */
    BYTE work[FF_MAX_SS]; /* Work area (larger is better for processing time) */


    /* Format the default drive with default parameters */
    res = f_mkfs("", 0, work, sizeof work);
    if (res) ...

    /* Give a work area to the default drive */
    f_mount(&fs, "", 0);

    /* Create a file as new */
    res = f_open(&fil, "hello.txt", FA_CREATE_NEW | FA_WRITE);
    if (res) ...

    /* Write a message */
    f_write(&fil, "Hello, World!\r\n", 15, &bw);
    if (bw != 15) ...

    /* Close the file */
    f_close(&fil);

    /* Unregister work area */
    f_mount(0, "", 0);

    ...