TFAT Registry Settings (Windows CE 5.0)

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The Transaction-Safe FAT (TFAT) file system retrieves driver specific settings from the registry. TFAT is a super-set of FATFS. While most TFAT registry settings are the same as those used for FATFS, some are unique to TFAT.

You can place settings for TFAT at two different FATFS tiers in the registry hierarchy

  • Root file system key

    Settings made at the root key of the file system registry, HKEY_LOCAL_MACHINE\System\StorageManager\FATFS, apply to every mounted instance of FATFS, unless explicitly overridden by a setting at a lower level. These setting apply to FATFS for all profiles.

  • Profile-specific settings

    Settings made at the Profiles registry subkey, HKEY_LOCAL_MACHINE\System\StorageManager\Profile\<MyProfileName>\FATFS, apply only to mounted instances of FATFS on devices that report the profile <MyProfileName>.

The following table shows the registry settings for the FAT file system that you can place in

HKEY_LOCAL_MACHINE\System\StorageManager\FATFS

- or -

HKEY_LOCAL_MACHINE\System\StorageManager\Profile\<MyProfileName>\FATFS.
Registry value: Type Description
BufferSize: REG_DWORD Specifies the number of sector-sized buffers to use for streams.

The default value is 64 for TFAT and 32 for FAT.
CacheSize: REG_DWORD This value is deprecated for Windows CE 5.0 and later. Replace with FatCacheSize or DataCacheSize.

Indicates the size of the disk cache, in number of sectors. This value must be a power of 2 and at least 16 sectors. If set to zero, FATFS will determine the best cache size to use.

For more information, see CacheSize registry subkey.
CodePage: REG_DWORD Overrides CP_OEMCP in all character conversions.
DataCacheSize: REG_DWORD Indicates the size of the data cache, in number of sectors. This value must be a power of 2 and at least 16 sectors. If set to zero, FATFS will determine the best cache size to use, up to twice the size of FatCacheSize.

For more information, see CacheSize registry subkey.
Dll: REG_SZ Specifies the name of the file system DLL.
EnableCache: REG_DWORD Controls caching.
  • 0 - Disables caching
  • 1 - Enables caching
EnableCacheWarm: REG_DWORD This value is deprecated for Windows CE 5.0 and later. Replace with EnableFatCacheWarm or EnableDataCacheWarm.

Set to 1 to enable pre-warming of the Fat cache. That is, the cache is pre-loaded to capacity with data on initialization.
EnableFatCacheWarm: REG_DWORD Set to 1 to enable pre-warming of the data cache. That is, the cache is pre-loaded to capacity with data on initialization. For example, if the cache is n sectors, the first n sectors of the cached region is read from disk.
EnableDataCacheWarm: REG_DWORD Set to 1 to enable pre-warming of the cache. That is, the cache is pre-loaded to capacity with data on initialization. For example, if the cache is n sectors, the first n sectors of the cached region is read from disk.
EnableWriteBack: REG_DWORD Enables a write-back or write-through cache. This setting applies only to Windows CE 5.0 and later.
  • 0 - Enables a write-through cache
  • 1 - Enables write-back cache
FatCacheSize: REG_DWORD Indicates the size of the FAT cache, in number of sectors. This value must be a power of 2 and at least 16 sectors. If set to zero, FATFS will determine the best cache size to use, based on size of the FATFS up to 512 sectors.

For more information, see CacheSize registry subkey.
Flags: REG_DWORD Indicates FAT file system registry flags. Default is 64.

For more information, see Flags registry subkey.
FormatTfat: REG_DWORD Set to 1 to format the volume as TFAT on auto-format or through IOCTL_DISK_FORMAT_VOLUME.
FriendlyName: REG_SZ Specifies a friendly name for the file system.
MountLabel: REG_DWORD Pulls the volume label and uses it as a mount point.
Paging: REG_DWORD Controls paging.
  • 0 - Disables paging
  • 1 - Enables paging
Util: REG_SZ Specifies the DLL name of utility to do format and scan.
MountFlags: REG_DWORD This value is deprecated for Windows CE 5.0 and later. For replacement values, see Mount Settings.
LazyWriterThreadPrio256: REG_DWORD Sets the priority of the lazy writer thread. Default is idle.

For more information, see Lazy-Writer Thread.

**Note   **When you enable pre-warming of the FAT or data cache, you trade longer boot times for quicker cache access when fully booted. To determine the settings that offer the best performance for your target device, experiment with different values for EnableFatCacheWarm and EnableDataCacheWarm.

Improving TFAT Performance

Registry hive files are memory-mapped, causing very slow performance with a registry hive on a TFAT volume. You can improve this performance by setting appropriate registry values.

The following list shows the registry keys that offer the greatest potential for improving performance.

  • FATFS_WFWS_NOWRITETHRU
  • EnableCache
  • EnableWriteBack
  • EnableFatCacheWarm
  • FatCacheSize
  • EnableDataCacheWarm
  • DataCacheSize

To obtain the greatest benefit from using these settings, measure performance before and after making a change, and test using scenarios that are important to your design.

Atomic Sector Writes

TFAT requires the underlying block structure to support atomic sector writes. The flash driver and most CF card hardware provide atomic sector write operations. In cases where the block driver is not atomic, TFAT cannot guarantee transaction safety.

The following settings are recommended for hard drives and other media with non-atomic sector writes:

[HKEY_LOCAL_MACHINE\System\StorageManager\Profiles\HDProfile\FATFS]
    "Flags"=dword:00280014

The following settings are recommended for storage media with atomic sector writes:

[HKEY_LOCAL_MACHINE\System\StorageManager\Profiles\<Profile Name>\FATFS]
    "Flags"=dword:00000014

Default TFAT Settings

The following registry key example is the default for the TFAT file system; profiles can override these values:

[HKEY_LOCAL_MACHINE\System\StorageManager\FATFS]
    "FriendlyName"="TFAT FileSystem"
    "Dll"="fatfsd.dll"
    "Flags"=dword:00000024
    "Paging"=dword:1
    "CacheSize"=dword:0

Flags registry subkey

The following table shows the available values you can set for the Flags registry subkey; set Flags to a combination of these values.

Flag Value Description
FATFS_UPDATE_ACCESS 0x00000001 Updates access times.
FATFS_DISABLE_LOG 0x00000002 Disables event logging.
FATFS_DISABLE_AUTOSCAN 0x00000004 Disables automatic calls to ScanVolume.
FATFS_VERIFY_WRITES 0x00000008 Verifies all writes.
FATFS_ENABLE_BACKUP_FAT 0x00000010 Adds a backup FAT to all formats.
FATFS_FORCE_WRITETHROUGH 0x00000020 Sets all files to WRITE_THROUGH, regardless of the parameters to CreateFile.
FATFS_DISABLE_AUTOFORMAT 0x00000040 Disables automatic formatting of unformatted volumes.
FATFS_WFWS_NOWRITETHRU 0x00010000 Disables write through on the WriteFileWithSeek function. Improves memory-mapped file performance.
FATFS_DISABLE_FORMAT 0x00020000 Disables format.
FATFS_TRANS_DATA 0x00040000 Transacts data on a write operation.
FATFS_TFAT_NONATOMIC_SECTOR 0x00080000 Uses the cluster 1 entry in the FAT table for a TFAT transaction. TFAT uses the NOF field of the boot sector by default.
FATFS_DISABLE_TFAT_REDIR 0x00100000 Disables the redirect of the root directory to another hidden directory for FAT12 or 16.
FATFS_TFAT_ALWAYS 0x00200000 Marks transaction status, even if only one sector in FAT is changed.
FATFS_FORCE_TFAT 0x00400000 Forces TFAT transactions even if the volume is not formatted as TFAT.
FATFS_LFN_EXTENDED 0x00800000 Generate LFN entries for extended characters always
FATFS_TFAT_DISABLE_MOVEDIR 0x01000000 Disable movefile on a directory for TFAT because it isn't transaction-safe

See Also

Transaction-Safe FAT File System | FlushFileBuffers

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