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O'Reilly Network: Understanding Unix Filesystems

Mar 04, 2001, 20:14 (0 Talkback[s])
(Other stories by Dru Lavigne)

"In last week's article, we viewed a PC's BIOS partition table and its Unix partition table using the fdisk and disklabel utilities. Let's continue this week by looking at the newfs utility and inode tables. The newfs utility actually formats your slice with the filesystems you previously specified with the disklabel utility. Let's start by taking a closer look at formatting and filesystems in general so we can gain a better appreciation of newfs."

"There are two types of hard-drive formatting. When you purchased your hard drive, it most likely was already "low level" formatted for you by the manufacturer. Low-level formatting creates the tracks and sectors on the drive; the intersection of these tracks and sectors creates the units of storage known as physical blocks, which are 512 bytes in size."

"The second type of formatting is called "high-level" formatting. This type of formatting installs a particular file system onto a slice of your physical drive using a utility such as DOS's format or FreeBSD's newfs. Some examples of file systems are FAT16, FAT32, NTFS, and FFS. Different file systems may vary in performance, but they usually have two features in common:

  • They require some type of table to map block addresses to the files contained within the blocks
  • They may also use a "logical" block addressing scheme to try to optimize read/write performance"

"Let's pretend you're a file system for a moment."

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