File System Comparison

File systems are the architectural foundations upon which all persistent data storage rests. Every file you've ever saved, every database record ever committed, every configuration that survived a reboot—all exist because a file system organized raw storage blocks into meaningful, navigable structures.

Yet file systems differ dramatically in their capabilities, design philosophies, and target use cases. Choosing the right file system for a given scenario requires understanding not just what features exist, but why they matter and how they interact under real-world conditions.

This page provides a comprehensive feature comparison across the dominant file systems in modern computing: FAT (legacy compatibility), NTFS (Windows enterprise), ext4 (Linux workhorse), XFS (high-performance Linux), ZFS (enterprise data integrity), and Btrfs (Linux modern COW). By examining their individual capabilities systematically, you'll develop the mental framework needed to make informed storage decisions.

Before comparing specific file systems, we must establish a systematic framework for evaluation. File system features fall into distinct categories that reflect different aspects of storage management:

Fundamental Categories of File System Features:

The Evolution of Feature Sets:

File system features haven't appeared randomly—they evolved in response to specific technological shifts and user requirements:

• 1970s-1980s: Basic hierarchical organization (early Unix, FAT)—focus on simply making storage usable
• 1990s: Security and journaling (NTFS, ext3)—driven by enterprise reliability requirements
• 2000s: Scalability and performance (XFS, ext4)—responding to exploding data volumes
• 2010s-Present: Data integrity and flexibility (ZFS, Btrfs)—addressing bit rot, flash storage, and cloud integration

Each generation built upon previous foundations while introducing capabilities that earlier systems couldn't provide. Modern "next-generation" file systems like ZFS and Btrfs often combine features that required separate filesystems and volume managers in earlier eras.

How a file system organizes data on disk fundamentally shapes its performance characteristics, scalability limits, and operational behavior. Let's examine how each major file system approaches this critical design dimension.

Deep Dive: Allocation Strategies

The allocation strategy determines how disk blocks are assigned to files:

Cluster Chains (FAT): Each cluster contains a pointer to the next cluster in the FAT table. Simple implementation but terrible performance for large files—reading a 1GB file requires traversing thousands of FAT entries. Seek times dominate; no ability to preallocate contiguously.

Extent-Based Allocation (NTFS, ext4, XFS, Btrfs): Files are described by "extents"—contiguous runs of blocks described as (start_block, length). A 1GB contiguous file needs only one extent descriptor versus thousands of block pointers. Benefits:

• Dramatically reduced metadata overhead
• Enables efficient preallocation
• Substantial reduction in seek operations for sequential access

Copy-on-Write Extents (ZFS, Btrfs): Extents are immutable—modifications create new extents rather than overwriting existing ones. This enables:

• Atomic writes (never partial data on crash)
• Trivial snapshots (just keep old extent references)
• Natural deduplication (identical extents can be shared)

However, COW causes fragmentation over time as files are repeatedly modified in place.

Deep Dive: Directory Structures

Directory performance becomes critical when directories contain many entries:

Linear Lists (FAT, early Unix): Each lookup requires scanning all directory entries sequentially. O(n) lookup time makes directories with thousands of entries painfully slow. The Linux locate database exists partly because filesystem directory traversal was historically expensive.

Hash-Based Structures (ext4 HTree, ZFS ZAP): Filenames are hashed to locate directory entries in O(1) average time. ext4's HTree uses a multi-level hash table that scales to millions of entries. ZFS's ZAP (ZFS Attribute Processor) provides extensible hashing with dynamic resizing.

B-Tree Directories (NTFS, XFS, Btrfs): Directory entries are stored in balanced trees providing O(log n) lookup, insertion, and deletion. Consistent performance regardless of directory size. NTFS and XFS use B+ trees specifically, optimized for block-oriented disk I/O.

For directories with thousands or millions of entries (common in backup systems, mail servers, package managers), the difference between linear search and tree/hash lookup can be orders of magnitude.

Data integrity features protect against corruption from hardware failures, power losses, software bugs, and the gradual bit decay known as "bit rot." Different file systems offer dramatically different integrity guarantees.

¹ ReFS provides checksums for NTFS environments ² Windows Storage Spaces provides resilience at the volume layer

Understanding Journaling Variations:

Journaling protects filesystem consistency across crashes, but implementations vary significantly:

Metadata-Only Journaling (NTFS, XFS, ext4 ordered): Only filesystem metadata (inodes, directory entries, allocation bitmaps) is journaled. File contents may be inconsistent after crashes, but the filesystem structure remains navigable. This is sufficient for most scenarios and provides good performance.

Full Data Journaling (ext4 journal mode): Both metadata and file contents are written to the journal before being committed to their final locations. Maximum safety but roughly halves write performance (each block is written twice).

Intent Log (ZFS ZIL, Btrfs Log Tree): Transactions are logged to a dedicated log structure, but COW semantics mean data is never overwritten in place. The log primarily handles synchronous write performance; actual consistency comes from atomic pointer updates in the tree structure.

Copy-on-Write: Beyond Crash Consistency

Copy-on-write (COW) file systems never overwrite existing data—modifications create new blocks while preserving originals. This provides unique integrity benefits:

Atomic Updates: An entire transaction completes atomically by updating a single root pointer. Either all changes are visible, or none are. There's no window where partial writes exist on disk.

No Torn Writes: Traditional file systems can experience "torn writes" where a crash interrupts a multi-block write, leaving half-old and half-new data. COW eliminates this entirely—old data remains intact until new data is fully committed.

Snapshot Foundation: Since old data is preserved naturally, snapshots become trivial—just keep the old root pointer. This enables:

• Instantaneous backup points
• Rollback capabilities
• Space-efficient historical versioning

The Fragmentation Cost: COW's weakness is fragmentation. Repeatedly modifying the same file regions creates scattered blocks across the disk rather than maintaining contiguity. This is particularly problematic for:

• Database files with random updates
• Virtual machine images
• Log files with append-heavy patterns

Access control determines who can read, write, execute, and manage files. The sophistication of these mechanisms varies dramatically across file systems, from FAT's complete absence of security to NTFS's elaborate permission model.

¹ dm-crypt/LUKS provides encryption at the block layer for Linux filesystems

Permission Model Comparison:

FAT32 (No Security): FAT32 has no concept of file ownership or permissions. Every user has full access to all files. This was acceptable for single-user systems but makes FAT32 unsuitable for any security-sensitive application. FAT is still used for removable media specifically because any system can read/write without permission complications.

Unix Traditional Permissions (ext4, XFS, Btrfs): The classic owner/group/others model with read/write/execute bits. Simple but limited:

• Only one owner, one group per file
• No way to grant access to multiple specific users
• Execute permission overloaded for directory traversal
• setuid/setgid bits enable privilege escalation

POSIX ACLs extend this with per-user and per-group entries, enabling granular control without the rigidity of the basic model.

NTFS Permissions: NTFS provides elaborate permission inheritance with:

• Per-object security descriptors
• Fine-grained permission types (Read Data, Write Data, Create Files, Delete, Take Ownership, etc.)
• Inheritance rules from parent containers
• Ownership and primary group metadata
• Integrity levels for Vista+ mandatory access control

This complexity enables precise enterprise security but creates administrative burden and potential for misconfiguration.

Encryption Approaches:

NTFS EFS (Encrypting File System): Per-file encryption using user certificates. Files are transparently decrypted when accessed by authorized users. Integrated with Windows authentication. Recovery agents can access encrypted files if user credentials are lost.

ZFS Native Encryption: Dataset-level encryption with inheritance. Keys are managed separately from the data, enabling encrypted send/receive operations. Encryption is AES-256-GCM by default. Keys can be wrapping keys, passphrases, or external key management.

Block-Layer Encryption (dm-crypt/LUKS, BitLocker): For filesystems without native encryption, block-layer solutions encrypt the entire device. This protects all data uniformly but doesn't support per-file or per-user encryption granularity. The filesystem itself is unaware of encryption.

The Trade-off: Filesystem-level encryption (EFS, ZFS) enables per-file policies and seamless backups of still-encrypted data. Block-level encryption is simpler and filesystem-agnostic but operates at a coarser granularity.

Beyond basic file storage, modern file systems provide sophisticated features that transform raw storage into intelligent data services. These features often differentiate enterprise-grade systems from consumer-oriented alternatives.

¹ ReFS and Storage Spaces provide deduplication for Windows ² Can use SquashFS for read-only compressed filesystems

Compression Deep Dive:

NTFS Compression: NTFS uses LZ compression on a per-file basis, enabled via file attributes. Compression happens transparently on read/write. Works well for text and documents but adds CPU overhead. Compressed files suffer fragmentation as they grow, since compressed size is unpredictable.

ZFS Compression: Dataset-level compression with algorithm selection per-dataset. LZ4 (fast, moderate compression) is the default. ZSTD provides excellent compression with reasonable performance. GZIP maximizes compression at CPU cost. Compression is applied per-block, so random access remains efficient.

Compression in ZFS often improves performance because:

• Less data transferred from disk
• Modern CPUs compress faster than disks can read
• Reduced write amplification on SSDs

Btrfs Compression: Similar to ZFS with algorithm selection. ZSTD support is mature. Can be per-file or per-subvolume via mount options or properties.

Snapshots and Clones:

Volume Shadow Copy (NTFS/Windows): VSS provides point-in-time snapshots at the volume level. Used for:

• Backup coordination (consistent backup points)
• Previous Versions feature (user-accessible file recovery)
• System Restore points

VSS uses copy-on-write at the block level through a system driver, not native filesystem features.

ZFS Snapshots: Instantaneous, space-efficient, hierarchical. Creating a snapshot is a metadata operation that completes in milliseconds regardless of data size. Snapshots consume only the space of changed blocks. Use cases:

• Pre-upgrade safety points
• Consistent backup sources
• Development/test environment resets
• Ransomware recovery

Clones are writable copies derived from snapshots, sharing unchanged blocks with the original.

Btrfs Subvolume Snapshots: Similar to ZFS but organized around subvolumes. Each snapshot is itself a subvolume that can be mounted, modified (if not read-only), or snapshotted further. Common layouts use @root and @home subvolumes with separate snapshot schedules.

Having examined individual feature categories, let's synthesize this knowledge into a comprehensive comparative view that highlights each file system's overall feature profile.

Key Observations:

FAT32 — Maximum Compatibility: FAT32 lacks every advanced feature but remains essential because it's the only filesystem universally readable by all operating systems and devices. USB drives, SD cards, and cross-platform media almost always use FAT32 (or exFAT for larger files).

NTFS — Windows Enterprise Standard: NTFS provides comprehensive feature coverage within the Windows ecosystem. Its learning curve is substantial, but its permission model, journaling, and integration with Windows services make it the only reasonable choice for Windows system drives.

ext4 — Linux Reliability: ext4 is the conservative choice for Linux—well-tested, performant, and universally supported. It lacks modern features like checksums and snapshots but compensates with maturity and tooling.

XFS — Scalability Focus: XFS excels at handling extremely large filesystems and files with consistent performance. Its recent addition of reflinks brings modern capabilities while maintaining its enterprise heritage.

ZFS — Data Integrity Leader: ZFS offers the most comprehensive feature set but requires significant RAM and careful planning. It's the gold standard for data that must never be corrupted or lost, despite not being mainstream in Linux distributions.

Btrfs — Linux Modern Alternative: Btrfs brings ZFS-like features to native Linux but with a more complex stability story. Some features (snapshots, compression) are production-ready; others (RAID5/6) remain problematic.

We've conducted a systematic examination of file system features across six major systems. Let's consolidate the essential takeaways:

What's Next:

Feature availability is only one dimension of file system comparison. The next page examines Performance Characteristics—how these file systems behave under different workloads, where their architectural choices translate to measurable speed differences, and what performance metrics actually matter for various use cases.