Chapter 12 -- File Systems

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Chapter 12

In this chapter, we present an overview of the file system formats supported by Microsoft Windows 2000. We then describe the types of file system drivers and their basic operation, including how they interact with other system components such as the memory manager and the cache manager. Windows 2000 includes a native file system format, called the NTFS file system. In the balance of the chapter, we focus on the on-disk layout of NTFS volumes and the advanced features of NTFS, such as compression, recoverability, quotas, and encryption.

To fully understand this chapter, you should be familiar with the terminology introduced in Chapter 10, including the terms volume and partition. You'll also need to be acquainted with these additional terms:

• Sectors are hardware-addressable blocks on a storage medium. Hard disks for x86 systems almost always define a 512-byte sector size. Thus, if the operating system wants to modify the 632nd byte on a disk, it must write a 512-byte block of data to the second sector on the disk.
• File system formats define the way that file data is stored on storage media and impact a file system's features. For example, a format that doesn't allow user permissions to be associated with files and directories can't support security. A file system format can also impose limits on the sizes of files and storage devices that the file system supports. Finally, some file system formats efficiently implement support for either large or small files or for large or small disks.
• Clusters are the addressable blocks that many file system formats use. Cluster size is always a multiple of the sector size, as shown in Figure 12-1. File system formats use clusters to manage disk space more efficiently; a cluster size that is larger than the sector size divides a disk into more manageable blocks. The potential trade-off of a larger cluster size is wasted disk space, or internal fragmentation, that results because file sizes typically aren't perfect multiples of cluster sizes.



Figure 12-1 Sectors and a cluster on a disk

• Metadata is data stored on a volume in support of file system format management. It isn't typically made accessible to applications. Metadata includes the data that defines the placement of files and directories on a volume, for example.