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Overview

How Does the System Work​

MooseFS provides a distributed storage architecture designed to be powerful, scalable, and fully transparent to the user. While it operates behind the scenes with multiple interacting components, from the user's perspective, working with MooseFS is just like using any standard POSIX-compliant file system.

Transparent Operation via FUSE and mfsmount​

When a client mounts a MooseFS volume using mfsmount, it leverages FUSE (Filesystem in Userspace) to intercept file operations initiated by the operating system’s kernel. These operations are passed to the mfsmount process, which then communicates over the network with the Master Server and Chunkservers.

This architecture ensures that all standard file operations - such as opening, reading, writing, renaming, or deleting files - function exactly as they would on a local file system. The complexity of distributed data management remains hidden from the user.

Communication with the Master Server​

The Master Server is responsible for handling all metadata-related operations. Each time a client performs an action that affects file structure or attributes, mfsmount contacts the Master Server. Examples include:

  • Creating or deleting files and directories
  • Reading directory contents
  • Changing file attributes (e.g., permissions, timestamps)
  • Modifying file sizes
  • Initiating read or write operations
  • Accessing special files (such as those under MFSMETA)

By centralizing metadata management, MooseFS ensures consistency and coordination across the cluster.

Direct Data Access via Chunkservers​

Actual file data is stored across multiple Chunkservers in the form of chunks. When reading or writing data, mfsmount connects directly to the relevant Chunkserver(s) that store the necessary chunks. This bypasses the Master Server for data transfers, significantly improving performance and reducing bottlenecks.

After a write operation completes, the client notifies the Master Server so it can update metadata, including file length and last modification time.

Chunkserver Replication and Data Redundancy​

To meet redundancy and fault tolerance requirements, Chunkservers communicate with each other to replicate file chunks. MooseFS ensures that the number of chunk copies on different Chunkservers matches the configured redundancy level. This background replication process provides resilience against hardware failures, ensuring data availability even when one or more storage nodes go offline.