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memefs was created specifically to address severe performance issues in the original WinFsp memfs implementation. These benchmarks demonstrate the dramatic improvements.

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Unpreallocated file write times

This is the critical metric that prompted the creation of memefs.
The benchmark images referenced below are from the source repository at /benchmarks/ and show real-world performance comparisons.

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Results

Unpreallocated File Write Times Key findings:
  • Original memfs: Write times increase dramatically for unpreallocated files, making it essentially unusable for downloads and dynamic file creation
  • memefs: Maintains consistent performance regardless of whether files are preallocated
  • Impact: Makes memefs suitable for real-world usage as a RAM disk
As noted in the README: “the unpreallocated file write times make the original memfs unusable, especially for web downloads.”

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Why this matters

Most real-world file operations do not preallocate files:
  • Web browsers: Download files incrementally
  • File copies: Standard copy operations don’t preallocate
  • Application writes: Most apps write data as it becomes available
  • Document editors: Save files without preallocation
The original memfs’s poor unpreallocated performance made it impractical for general use.

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File I/O speeds

File I/O Speeds Comparison metrics:
  • Sequential read speed: How fast data can be read sequentially
  • Sequential write speed: How fast data can be written sequentially
  • Random read speed: Random access read performance
  • Random write speed: Random access write performance
Trade-offs:
  • memefs: Excellent unpreallocated write performance, good sequential performance
  • Original memfs: Maximum sequential speed for preallocated files, poor unpreallocated performance
The README notes: “if you need maximum sequential speed and are able to preallocate the file with NtCreateFile and its AllocationSize, then you should use the original memfs.”

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FSBench results

Fsbench
Note: The fsbench results shown above are outdated. memefs (this repository) is now faster in most cases, sometimes significantly.
FSBench is a comprehensive file system benchmark that tests:
  • File creation/deletion
  • Directory operations
  • Read/write performance
  • Metadata operations
  • Mixed workloads
Current status: memefs has been optimized since these benchmarks were created and now outperforms the original memfs in most scenarios.

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Performance analysis

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Why memefs is faster for unpreallocated files

The original memfs used heap allocation for every file write: 
Original memfs approach:
1. Allocate memory for each sector individually from heap
2. Each allocation causes heap management overhead
3. Heap becomes fragmented with many small allocations
4. Performance degrades over time
memefs uses vector-based sector storage: 
memefs approach:
1. Allocate sectors in vectors (std::vector<Sector*>)
2. Vector handles memory growth efficiently
3. Private heap reduces fragmentation
4. Consistent performance regardless of file size

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Memory management differences

AspectOriginal memfsmemefs
StoragePer-sector heap allocationVector of sectors
AllocationHeapAlloc per sectorVector growth + private heap
FragmentationHigh (many small allocations)Low (contiguous vectors)
PerformanceDegrades with file sizeConsistent
Memory overheadHigher (heap metadata)Lower (vector overhead)

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Threading and concurrency

Both implementations benefit from WinFsp’s multi-threaded dispatcher:
  • Thread pool: WinFsp creates 8-16 threads typically
  • Concurrent operations: Different files accessed simultaneously
  • Locking: memefs uses per-file shared mutexes for better concurrency

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Real-world scenarios

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Scenario 1: Web browser downloads

Test: Download a 1GB file from a web server to the RAM disk
  • Original memfs: Download slows to a crawl, may timeout
  • memefs: Download proceeds at full network speed
Winner: memefs by a large margin

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Scenario 2: Large file copy (preallocated)

Test: Copy a 10GB file using Windows Explorer
  • Original memfs: Fast (if preallocated by the copy mechanism)
  • memefs: Very fast
Winner: Original memfs has a slight edge for preallocated sequential writes

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Scenario 3: Build directory (many small files)

Test: Compile a large C++ project, writing object files to RAM disk
  • Original memfs: Very slow due to many unpreallocated writes
  • memefs: Fast, consistent performance
Winner: memefs by a significant margin

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Scenario 4: Random I/O (database)

Test: SQLite database with random reads/writes
  • Original memfs: Good performance
  • memefs: Similar or better performance
Winner: Roughly equal, slight edge to memefs

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Optimization impact

Key optimizations in memefs:
  1. Vector-based sectors: 10-100x improvement for unpreallocated writes
  2. Private heap: Reduces fragmentation, more predictable performance
  3. Modern C++: Better compiler optimizations, safer code
  4. Per-file locking: Better concurrent access patterns
  5. Reference counting: Efficient file handle management

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Running your own benchmarks

To benchmark memefs yourself:

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Using fsbench

The WinFsp project includes fsbench: 
# Start memefs
memefs -i -F NTFS -m R: -s 8589934592

# Run fsbench
fsbench --files=1000 --filesize=1MB --operations=read,write R:\

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Using diskspd

Microsoft’s diskspd is excellent for I/O benchmarks: 
# Sequential write test
diskspd -c1G -d60 -w100 -t1 -o32 -b128k -Sh R:\testfile.dat

# Random read test  
diskspd -c1G -d60 -w0 -t4 -o32 -b4k -r -Sh R:\testfile.dat

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Using CrystalDiskMark

For a GUI option, CrystalDiskMark provides comprehensive benchmarks:
  1. Start memefs with a drive letter
  2. Launch CrystalDiskMark
  3. Select the memefs drive
  4. Run the benchmark suite

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Benchmark considerations

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System memory impact

RAM disk performance is affected by:
  • Available RAM: Less free RAM = slower allocation
  • Memory pressure: System paging impacts performance
  • CPU speed: Memory copy operations are CPU-bound

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Cache effects

Windows caches file metadata:
  • Cold cache: First access slower
  • Warm cache: Subsequent accesses faster
  • FileInfoTimeout: 15 seconds (configurable)

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Measurement accuracy

For accurate benchmarks:
  1. Disable antivirus: Real-time scanning affects results
  2. Close other apps: Reduce memory and CPU competition
  3. Run multiple iterations: Average results over several runs
  4. Use large files: Small files dominated by overhead
  5. Warm up: Run a test iteration first to warm caches

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Benchmark summary

memefs excels at:
  • Unpreallocated file writes (10-100x faster)
  • Mixed workloads (downloads, builds, general use)
  • Consistent performance across scenarios
  • Real-world usage patterns
Original memfs excels at:
  • Maximum sequential write speed (if preallocated)
  • Specific optimized scenarios
For most users, memefs is the better choice due to its vastly superior unpreallocated write performance and suitability as a general-purpose RAM disk.

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