HAMMER File System
HAMMER is a next-generation file system developed for the DragonFly BSD operating system. It is designed for high performance, data integrity, and scalability, offering features like snapshots, history retention, and fine-grained management of storage. Here's a detailed look at HAMMER and its features:
Structure of the HAMMER File System
1. Master Blocks:
HAMMER uses master blocks to store metadata about the file system:
Volume Information:Contains data about the physical storage devices and volume configuration.
Root B-Tree:Points to the root of the B-Tree structure, which manages metadata and file data.
Undo Log:Tracks changes for transaction consistency and recovery.
2. B-Tree Structure:
HAMMER organizes metadata and data using a B-Tree:
Internal Nodes:
Store pointers to child nodes for quick lookups.
Leaf Nodes:
Contain actual file and directory metadata, as well as references to data blocks.
3. Snapshots and History:
HAMMER includes built-in support for snapshots and historical data:
Snapshots:
Instantaneous, read-only copies of the file system.
History Retention:
Tracks changes over time, allowing recovery of previous versions of files.
4. Transactional Integrity:
HAMMER ensures data consistency through its transactional model:
Undo Logs:
Changes are recorded in undo logs before being committed to the main file system.
Crash Recovery:
Ensures that incomplete transactions are rolled back after a crash.
Features of HAMMER
Snapshots and History:
Create point-in-time snapshots and maintain a history of changes for data recovery.
Deduplication:
Identifies and eliminates duplicate blocks to save storage space.
Large Volume Support:
Designed to handle file systems up to 1 exabyte in size.
Clustered Storage:
Built with future support for clustered file systems.
Fine-Grained Filesystem Management:
Tools for pruning historical data and managing storage efficiency.
Limitations of HAMMER
Single-Master Design:
Currently supports only single-master configurations, limiting multi-node scalability.
Complex Administration:
Advanced features may require expertise for effective management.
Write Performance:
Snapshot and history features can introduce performance overhead in write-heavy workloads.
Tools and Commands for HAMMER
hammer:Primary tool for managing HAMMER file systems.
hammer cleanup:Prunes old history and reclaims storage space.
hammer snap:Creates snapshots of the file system.
hammer show:Displays detailed file system information.
Example
HAMMER is a powerful file system with features tailored for data integrity, recovery, and efficient management of large-scale storage. Its advanced capabilities make it an excellent choice for enterprise and data-centric environments.