UNIX/Linux File System

What file system is standard in UNIX/Linux?

The ext file system, which uses a multilevel index scheme with metadata stored in inodes.

Where is file metadata stored in UNIX/Linux?

In an inode, a table entry referenced by an i-number (inode number) from a directory.

What is not stored in an inode?

The file name—names are stored in directory entries, allowing aliases (multiple names pointing to the same inode).

How does UNIX manage file deletion?

The inode tracks a reference count of directory entries pointing to it. The file is only deleted when this count reaches zero.

What is the structure of a UNIX inode?

A hybrid indexed structure with:

1. Direct pointers (10–13) to data blocks.

2. A single index block (for larger files).

3. A double index block (pointing to index blocks).

4. A triple index block (for very large files, supporting up to 4TB).

How does UNIX optimize small file access?

The inode is loaded into memory when a file is opened, providing immediate access to direct pointers for small files.

How does the single index block work?

It contains pointers (e.g., 1,024 for 4KB blocks) to additional data blocks.

How does the double index block work?

It points to index blocks, which then point to data blocks (supporting ~1 million data blocks).

How does the triple index block work?

It points to double index blocks, enabling addressing of over 4TB of data (with 4KB blocks).

How are inodes allocated during file system initialization?

The i-list is sized for the disk partition, with empty inodes distributed evenly to localize file blocks near their inodes.

Why does UNIX place file blocks near their inodes?

To minimize seek time by keeping related data close, assuming other processes aren’t accessing distant files.