FAT File System Registry Settings (Windows CE 5.0)
The file allocation table file system (FATFS) retrieves driver specific settings from the registry.
You can place FATFS settings at two different 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 locally. That is, settings at this registry key 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.
|
| 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. For example, if the cache is n sectors, the first n sectors of the cached region is read from disk. |
| 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. |
| 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 | Formats the volume as TFAT on auto-format or through IOCTL_DISK_FORMAT_VOLUME. |
| FriendlyName: REG_SZ | Specifies a friendly name for the file system. |
| MountFlags: REG_DWORD | This value is deprecated for Windows CE 5.0 and later. For replacement values, see Mount Settings. |
| MountLabel: REG_DWORD | Pulls the volume label and uses it as a mount point. |
| Paging: REG_DWORD | Controls paging.
|
| Util: REG_SZ | Specifies the DLL name of utility to do format and scan. |
| 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.
Default FATFS Settings
The following registry key example is the default for the FAT file system; profiles can override these values:
[HKEY_LOCAL_MACHINE\System\StorageManager\FATFS]
"FriendlyName"="FAT 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 |
CacheSize registry subkey
The CacheSize registry subkey is a hexadecimal number of sectors to cache. This has to be a power of two. The following table shows valid numbers for the CacheSize registry subkey.
| Registry entry | Number of sectors | Cache in kilobytes (KB) |
|---|---|---|
| 2 | 2 | 1 |
| 4 | 4 | 2 |
| 8 | 8 | 4 |
| 10 | 16 | 8 |
| 20 | 16 | 32 |
| 40 | 64 | 32 |
| 80 | 128 | 64 |
| 100 | 256 | 128 |
| 200 | 512 | 256 |
| 400 | 1024 | 512 |
| 800 | 2048 | 1024 |
| 1000 | 4096 | 2048 |
See Also
File System Driver Creation | File System Driver Loading | Storage Manager | File System Filters | Block Drivers
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