CS-3310 - 04 I/O and Disks - Filesystem Implementations

What are the main on-disk structures of a file system?

Superblock, inode table, data region, and allocation structures (free lists or bitmaps).

What is the superblock?

A metadata block that stores global information about the file system (size, number of inodes, data blocks, etc.).

What is an inode?

A structure storing metadata and block pointers for a file.

Why are inodes important?

They separate file metadata from directory names and link the logical file to physical disk blocks.

What are direct pointers in an inode?

Pointers that directly reference data blocks.

What are indirect pointers?

Pointers that reference blocks containing more pointers, used for large files.

What is the data region?

The portion of disk where file contents are stored.

How does the OS keep track of free blocks?

Using free lists or bitmaps.

What is a directory's internal structure?

A list of (file name, inode number) pairs.

Why does deleting files leave gaps in directories?

Because entries are removed, leaving unused slots that can later be reused.

What is FAT (File Allocation Table)?

A table that keeps track of linked blocks for each file; used in older systems like MS-DOS.

What is a disadvantage of linked-list-based allocation?

Slow random access since you must traverse links sequentially.

How does FAT improve upon simple linked allocation?

Stores the link information in memory, enabling faster random access.

What is crash consistency?

The property that file systems remain in a valid state even after a crash or power loss.

What is fsck?

A file system checker that repairs inconsistencies between free lists, inodes, and directory entries.

What is journaling in file systems?

Logging intended changes before applying them, allowing recovery after a crash.

What does it mean for operations to be idempotent?

They can be repeated safely without changing the final result.

Why are backups important?

They allow recovery from both system failures and user mistakes.

What is an incremental backup?

A backup that saves only the data changed since the last backup.

What are the two kinds of backups?

Physical dumps (block-based) and logical dumps (file-based).

What is the main structure of the MS-DOS file system?

Fixed-size directory entries and FAT for tracking clusters.

What is the maximum theoretical file size in FAT32?

4 GB.

What does the UNIX v7 file system use for addressing?

Single, double, and triple indirect blocks.

What is ISO 9660?

A standard for CD-ROM file systems designed for maximum compatibility.

What are Rock Ridge extensions?

ISO 9660 extensions to support UNIX features like permissions and symbolic links.

What is Joliet?

A Microsoft extension to ISO 9660 that allows long Unicode filenames and deeper directories.