WINDOWS 1002000 PROFESSIONAL RESOURCE KIT [Electronic resources] نسخه متنی

File System Comparisons

You can use FAT16, FAT32, NTFS, or a combination of file systems on a single computer, but each volume can have only one file system installed. When choosing which file system to use, you need to determine the following:

How the computer is used (dedicated to Windows 2000 or multiple-boot).

The number and size of locally installed hard disks.

Security considerations.

Interest in using advanced file system features.

IMPORTANT

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It is recommended that you format all Windows 2000 volumes with NTFS except on computers with certain multiple-boot configurations. For more information about NTFS, see "NTFS File System" later in this chapter.

Certain file systems have limitations regarding the minimum and maximum size of volumes that they can format. Additionally, the cluster size of each file system, which depends on the size of the volume and the maximum number of clusters the file system can manage, can affect the choice of file systems.

Table 17.2 provides a comparison of FAT16, FAT32, and NTFS volume and cluster sizes.

Table 17.2 Default Cluster Sizes for Volumes with Windows 2000 File Systems

The following are some file system size limitations that should also be considered:

FAT volumes smaller than 16 megabytes (MB) are formatted as FAT12.

FAT16 volumes larger than 2 gigabytes (GB) are not accessible from computers running MS-DOS, Windows 95, Windows 98, and many other operating systems.

While FAT32 volumes can theoretically be as large as 2 terabytes, Windows 2000 limits the maximum size FAT32 volume that it can format to 32 GB. however, Windows 2000 can read and write to larger FAT32 volumes formatted by other operating systems.

The implementation of FAT32 in Windows 2000 limits the maximum number of clusters on a FAT32 volume that can be mounted by Windows 2000 to 4,177,918. this is the maximum number of clusters on a FAT32 volume that can be formatted by Windows 98.

NTFS volumes can theoretically be as large as 16 exabytes (EB), but the practical limit is 2 terabytes.

The user can specify the cluster size when an NTFS volume is formatted. however, NTFS compression is not supported for cluster sizes larger than 4 kilobytes (KB).

NOTE

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Clusters are also known as allocation units.

Comparing FAT File Systems

The numerals in the names FAT12, FAT16, and FAT32 refer to the number of bits required for a file allocation table entry.

FAT12 uses a 12-bit file allocation table entry (2¹² clusters).

FAT16 uses a 16-bit file allocation table entry (2¹⁶ clusters).

FAT32 uses a 32-bit file allocation table entry. However, Windows 2000 reserves the first 4 bits of a FAT32 file allocation table entry, which means FAT32 has a theoretical maximum of 2²⁸ clusters.

NOTE

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FAT12 is only used on floppy disks and on very small volumes in Windows 2000.

There are additional relative advantages and disadvantages between FAT16 and FAT32.

Advantages of FAT16

Advantages of FAT16 include:

MS-DOS, Windows 95, Windows 98, Windows NT, Windows 2000, and some unix operating systems can use FAT16.

There are many software tools that can address problems and recover data on FAT16 volumes.

If you have a startup failure, you can start the computer by using an MS-DOS bootable floppy disk to troubleshoot the problem.

FAT16 is efficient, in speed and storage, on volumes smaller than 256 MB.

Disadvantages of FAT16 include:

The root folder can manage a maximum of 512 entries. The use of long file names (LFNS) can significantly reduce the number of available entries.

FAT16 is limited to 65,536 clusters, but because certain clusters are reserved, it has a practical limit of 65,524. The largest FAT16 volume on Windows 2000 is limited to 4 GB and uses a cluster size of 64 KB. To maintain compatibility with MS-DOS, Windows 95, and Windows 98, a volume cannot be larger than 2 GB.

FAT16 is inefficient on larger volume sizes, as the size of the cluster increases. The space allocated for storing a file is based on the size of the cluster allocation granularity, not the file size. For example, a 10-KB file stored on a 1.2-GB volume, which uses a 32-KB cluster, wastes 22 KB of disk space.

The boot sector is not backed up.

There is no built-in file system security or compression scheme with FAT16.

FAT32 has the following enhancements:

The root folder on a FAT32 drive is an ordinary cluster chain and can be located anywhere on the volume. For this reason, FAT32 does not restrict the number of entries in the root folder.

FAT32 uses smaller clusters (4 KB for volumes up to 8 GB), so it allocates disk space more efficiently than FAT16. Depending on the size of your files, FAT32 creates the potential for tens and even hundreds of megabytes of additional free disk space on larger volumes compared to FAT16.

FAT32 can automatically use the backup copy of the file allocation table instead of the default copy (with FAT16, only a disk repair tool such as chkdsk can implement the backup).

The boot sector is automatically backed up at a specified location on the volume, so FAT32 volumes are less susceptible to single points of failure than FAT16 volumes.

Disadvantages of FAT32 include:

The largest FAT32 volume that Windows 2000 can format is 32 GB.

FAT32 volumes are not directly accessible from operating systems other than Windows 95 OSR2 and Windows 98.

If you have a startup failure, you cannot start the computer by using an MS-DOS or Windows 95 (excluding version OSR2 and later) bootable floppy disk.

There is no built-in file system security or compression scheme with FAT32.

The version of NTFS included with Windows 2000 can take advantage of many advanced features not available by using other file systems. As such, using NTFS wherever possible is recommended to gain the maximum benefits from Windows 2000.

Advantages of NTFS

Formatting Windows 2000 volumes with NTFS instead of FAT allows you to use advanced features that are available only on NTFS, including the following:

NTFS is a recoverable file system. a user seldom needs to run a disk repair program on an NTFS volume. NTFS guarantees the consistency of the volume by using standard transaction logging and recovery techniques. In the event of a system failure, NTFS uses its log file and checkpoint information to automatically restore the consistency of the file system.

NTFS supports compression on volumes, folders, and files. Files that are compressed on an NTFS volume can be read and written by any Windows-based application without first being decompressed by another program; decompression happens automatically during the file read. The file is compressed again when it is closed or saved.

NTFS supports all Windows 2000 file system features.

NTFS does not restrict the number of entries in the root folder.

Windows 2000 can format volumes up to 2 terabytes with NTFS.

NTFS manages disk space more efficiently than FAT, using smaller clusters (4 KB for volumes up to 2 terabytes).

The boot sector is backed up to a sector at the end of the volume.

NTFS minimizes the number of disk accesses required to find a file.

On NTFS volumes, you can set permissions on shares, folders, and files that specify which groups and users have access, and what level of access is permitted. NTFS file and folder permissions apply to users working on the local computer and to users accessing the file over the network from a shared folder. You can also set share permissions that operate on network shares in combination with file and folder permissions.

NTFS supports a native encryption system, EFS, that uses symmetric key encryption in conjunction with public key technology to prevent unauthorized access to file contents.

Reparse points enable new features such as volume mount points.

Disk quotas can be set to limit the amount of space users can consume.

NTFS uses a change journal to track changes made to files.

NTFS supports distributed link tracking to maintain the integrity of shortcuts and OLE links.

NTFS supports sparse files so that very large files can be written to disk while requiring only a small amount of storage space.

While NTFS is recommended for most Windows 2000 users, it is not appropriate in all circumstances. Disadvantages of NTFS include:

NTFS volumes are not accessible from MS-DOS, Windows 95, or Windows 98. The advanced features of the version of NTFS included with Windows 2000 are not available in Windows NT.

For very small volumes that contain mostly small files, the overhead of managing NTFS can cause a slight performance drop in comparison to FAT.

A former disadvantage of NTFS was accessing the NTFS-formatted system volume when corrupted or deleted system files prevented the computer from starting. In the past, it was a common requirement that Windows NT be installed to a second, separate folder to access the NTFS system volume of the first installation.

Windows 2000 resolves this problem by offering a pair of new troubleshooting tools. The first tool, known as Safe Mode, allows Windows 2000 to be started with only the basic set of device drivers and system services loaded. Safe Mode allows a system that cannot start, due to system corruption or the installation of incompatible drivers or system services, to bypass those blocking issues, enabling the local administrator to resolve the problem.

If the damage to the operating system files is severe enough that the computer cannot start even in Safe Mode, you can start the computer from either the Windows 2000 operating system CD or Setup floppy disks by using the Recovery Console. The Recovery Console is a special command-line environment that enables the administrator to copy system files from the operating system CD, fix disk errors, and otherwise troubleshoot system problems without installing a second copy of the operating system. For more information about Safe Mode and the Recovery Console, see "Troubleshooting Tools and Strategies" in this book.

Formatting the System Volume in Multiple-Boot Configurations

If you want to start another operating system, such as Windows 95, Windows 98, Microsoft® Windows® for Workgroups, or MS-DOS, use FAT16 for your system volume and the boot volumes for the other operating systems. You can use NTFS for the Windows 2000 boot volume and other volumes on the computer, if those volumes cannot be accessed by an operating system other than Windows 2000.

Performance

For small volumes, FAT16 or FAT32 might provide nominally faster access to files than NTFS because:

The FAT structure is simpler.

The FAT folder size is smaller for an equal number of files.

FAT has no controls regulating whether a user can access a file or a folder; therefore, the system does not have to check that a user has access permissions to a file or folder. This advantage is minimal, however, because Windows 2000 still must determine whether the file is read-only, or whether the file is on a FAT or NTFS volume.

NTFS minimizes the number of disk accesses and time needed to find a file. In addition, if a folder is small enough to fit in the Master File Table (MFT) record, NTFS reads the entire folder when it reads its MFT record.

A FAT folder entry contains an index of the file allocation table, which identifies the cluster number for the first cluster of the folder. To view a file, FAT has to search the folder structure.

For operations performed on large folders containing both long and short file names, the speed of a FAT operation depends on the operation itself and the size of the folder. If FAT searches for a file that does not exist, it needs to search the entire folder— an operation that takes longer on a FAT structure than on the structure used by NTFS.

Several factors affect the speed with which Windows 2000 reads or writes a file:

If a file is badly fragmented, NTFS usually requires fewer disk accesses than FAT to find all of the fragments.

For both file systems, the default cluster size depends on the volume size, and is always a power of 2. FAT16 addresses are 16 bits, FAT32 addresses are 32 bits, and NTFS addresses are 64 bits.

The default cluster size for a FAT16 volume is always larger than the default cluster size for either a FAT32 or an NTFS volume of the same size. The larger cluster size for a FAT16 volume, however, means that there might be less fragmentation in files on a FAT16 volume.

With NTFS, the MFT record can entirely contain small files; FAT contains pointers to files. The file size that fits within the MFT record depends on the cluster size and the number of attributes for the file.

On very large disks, the maximum size of a volume or file and the maximum number of files per volume depend on the file system used to format the volume.

NOTE

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Windows 2000 can combine noncontiguous disk areas when creating volume sets and stripe sets, but these volumes have the same maximum size limitations of a single volume.

Maximum Sizes on FAT16 Volumes

FAT16 can support a maximum of 65,524 clusters per volume. Table 17.3 lists FAT16 size limits.

IMPORTANT

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For Windows NT and Windows 2000, the cluster size of FAT16 volumes from 2 GB through 4 GB is 64 KB, which can create compatibility issues with some applications. For example, setup programs do not compute volume free space properly on a volume with 64 KB clusters and cannot run because of a perceived lack of free space. For this reason, either NTFS or FAT32 must be used on volumes larger than 2 GB. The Format tool in Windows 2000 displays a warning and asks for a confirmation before formatting a volume with 64 KB clusters.

Table 17.3 FAT16 Size Limits

Maximum Sizes on FAT32 Volumes

A FAT32 volume must have a minimum of 65,527 clusters. The maximum number of clusters that Windows 2000 can mount on a FAT32 volume is 4,177,918. Windows 2000 can format volumes up to 32 GB, but it can use larger volumes created by other operating systems. Table 17.4 lists FAT32 size limits.

Table 17.4 FAT32 Size Limits

Maximum Sizes on NTFS Volumes

In theory, the maximum NTFS volume size is 2⁶⁴ clusters. However, there are limitations to the maximum size of a volume, such as volume tables. By industry standards, volume tables are limited to 2³² sectors.

Sector size, another limitation, is typically 512 bytes. While sector sizes might increase in the future, the current size puts a limit on a single volume of 2 terabytes (2³² * 512 bytes, or 2⁴¹ bytes). For now, 2 terabytes is considered the practical limit for both physical and logical volumes using NTFS.

Table 17.5 lists NTFS size limits.

Table 17.5 NTFS Size Limits

Controlling Access to Files and Folders

On NTFS volumes you can set access permissions on files and folders that specify which groups and users have access, and what level of access is permitted. NTFS file and folder permissions apply to users on the local computer and to users accessing the file over the network. With NTFS you can also set share permissions, which operate on shared folders in combination with file and folder permissions. File attributes (read-only, hidden, and system) also limit file access.

File and Folder Permissions

The version of NTFS included with Windows 2000 provides for inheritable permissions. In the Properties dialog box, on the Security tab, you can set the option Allow inheritable permissions from parent to propagate to this file object. This option is enabled by default. This feature reduces the time and input/output (I/O) work required to change the permissions of many files and subfolders. For example, suppose a user wants to change the permissions on a tree consisting of several thousand files. If the folders and subfolders inherit permissions, the user only needs to set permissions for the top-level folder.

Figure 17.1 shows the permissions listed on the Security tab of the Properties dialog box of a DOC file.

Figure17.1 Permissions Dialog Box

Figure 17.2 shows the Permissions listed when you click Advanced on the Security tab of the Properties dialog box.

Figure17.2 Advanced Permissions Dialog Box

IMPORTANT

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To preserve permissions when you copy or move files between NTFS folders, use the Robocopy tool on the Windows 2000 Resource Kit companion CD.

You can back up and restore data on FAT and NTFS volumes. However, if you back up data from an NTFS volume and then restore it to a FAT volume, you lose security settings and other file information specific to NTFS.

Although NTFS provides access controls to individual files and folders, users can perform certain actions even if permissions are set on a file or folder to prevent access. For example, you have a folder (MyFolder) containing a file (File1), and you grant Full Control to a user for the folder MyFolder. If you specify that the user has No Access to File1, the user can still delete File1 because the Full Control rights in the folder allow the user to delete the contents of the folder.

To prevent files from being deleted, you must set permissions on the file itself, and you must set permissions for the folder containing the file that won't supercede the file's permissions. In the Properties dialog box, use the Security tab to deny Full Control, but to allow Modify, Read & Execute, Read, and Write permissions in place.

Anyone who has List, Read, or greater permissions in a folder can view file properties on any file in the folder, even if file permissions prevent them from seeing the contents of the file.

Share Permissions

FAT16 and FAT32 allow you to set limited file attributes but you cannot set permissions on individual files and folders. The only security available is the permissions that are set on the entire share, that affect all files and folders on that share, and that only functions over the network. After a folder is shared, you can protect the shared folder by specifying one set of share permissions for all files and subfolders of the shared folder. Share permissions are set in much the same way file and folder permissions are set in NTFS. But because share permissions apply globally to all files and folders in the share, they are significantly less versatile than the file and folder permissions used for NTFS volumes. Share permissions have no effect on users accessing the contents of a shared folder when the shared folder is on a locally-installed disk.

Share permissions apply equally to NTFS and FAT volumes. They are enforced by Windows 2000, not by the file system. However, when you move or copy a file from an NTFS to a FAT volume, permissions and other NTFS attributes are lost.

POSIX Compliance

NTFS provides Portable Operating System Interface for UNIX (POSIX) compliance, which permits UNIX programs to be ported to Windows 2000. Windows 2000 is fully compliant with the Institute of Electrical and Electronic Engineers (IEEE) standard 1003.1, which is a standard for file naming and identification.

The following POSIX-compliant features are included in NTFS:

Case-sensitive naming. For example, POSIX interprets README.TXT, Readme.txt, and readme.txt as separate files.

Hard links. A file can have more than one name. This allows two different file names, which can be in different folders, to point to the same data.

Additional time stamps. These show when the file was last accessed or modified.

CAUTION

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You must use POSIX-based programs to manage file names that differ only in case. You cannot use standard Windows 2000 command-line tools (such as copy, del, and move, or their equivalents in Windows Explorer) to manage file names that differ only in case. For example, if you type del MyDoc.Doc at the command prompt, both mydoc.doc and MyDoc.Doc are deleted.