Log-based File Systems

What problem do log-based file systems address?

They make file systems more resistant to failures/crashes by implementing transaction processing for metadata updates.

What happens when a traditional system crashes?

The OS runs a file system integrity checker before mounting the file system during the next boot.

What is the key concept behind transaction processing in file systems?

Updates must be atomic - either all changes reach disk or none do.

What are alternative names for log-based file systems?

Log-structured, transactional, or journaling file systems.

How does a log-based system handle metadata updates?

It first writes a record to a log file describing all planned updates before executing them.

What happens during system startup in a log-based file system?

The system checks the log for pending transactions and either completes them or aborts them if completion isn't possible.

What is the trade-off of using log-based file systems?

Increased data safety at the cost of decreased performance due to transaction logging.

What types of data are typically included in file system transactions?

Primarily metadata, though some OSs may include application data as well.

Why is the performance impact of logging considered acceptable?

Because alternative integrity checks after crashes could take hours on large systems, and single-user systems often have spare resources for logging.

What are examples of modern transaction-based file systems?

JFS (OS/2), HFS Plus (Mac), NTFS (Windows NT family), Ext3/ReiserFS/XFS/JFS (Linux).

What is the worst-case scenario when a transaction can't be completed?

Loss of the last block of data being written, but the file system remains uncorrupted.