RamDrive

A high-performance RAM disk for Windows, built with WinFsp and .NET 10. Mounts a virtual drive backed entirely by system memory for maximum I/O throughput.

Performance

Benchmarked with ATTO Disk Benchmark (Queue Depth 4):

I/O Size	Write (Direct I/O)	Read (Direct I/O)	Read (Cached)
64 KB	3.74 GB/s	4.67 GB/s	~9.5 GB/s
256 KB	6.47 GB/s	9.31 GB/s	~9.5 GB/s
1 MB	4.48 GB/s	3.51 GB/s	~9.5 GB/s

With EnableKernelCache: true (default), cached reads match kernel-mode ImDisk performance (~9.5 GB/s).

Architecture

WinFspRamAdapter (IFileSystem — all WinFsp callbacks, zero managed heap alloc on hot path)
    │
    ▼
RamFileSystem (path resolution, directory tree)
    │
    ▼
PagedFileContent (per-file page table: nint[])
    │
    ▼
PagePool (NativeMemory + ConcurrentStack<nint>)

Key design decisions:

• NativeMemory page pool -- all file data stored outside the GC heap via NativeMemory.AllocZeroed, zero GC pressure
• Lock-free page allocation -- ConcurrentStack<nint> with batch TryPopRange/PushRange for O(1) rent/return
• Per-file ReaderWriterLockSlim -- concurrent reads don't block each other
• Sparse files -- pages allocated on demand; unwritten regions consume no memory
• Write-lock minimization -- pages pre-allocated outside the lock, only memcpy inside
• Native AOT compiled -- single-file executable, no .NET runtime required

Quick Start

Option A: Installer (recommended)

1. Download RamDrive-X.Y.Z-setup.exe from Releases
2. Run the installer — it bundles WinFsp, configures the drive letter and capacity, and registers a Windows Service
3. The RAM disk starts automatically on boot

Option B: Portable

1. Download the .zip from Releases and extract
2. Install WinFsp 2.x manually
3. Run RamDrive.exe — press Ctrl+C to unmount

Configuration

Edit appsettings.jsonc or override via command line (--RamDrive:CapacityMb=4096):

{
  "RamDrive": {
    "MountPoint": "R:\\",           // Drive letter
    "CapacityMb": 2048,             // Total capacity in MB
    "PageSizeKb": 64,               // Page size (64 KB default, try 256 for large files)
    "PreAllocate": false,           // true = allocate all memory at startup
    "VolumeLabel": "RamDrive",      // Volume label in Explorer
    "EnableKernelCache": true,      // Kernel page cache (~3x read throughput)
    "InitialDirectories": {         // Directories created on mount
      "Temp": {}                    //   e.g. { "Temp": {}, "Cache": { "App1": {} } }
    }
  }
}

Formal Verification

The core concurrency protocol is formally verified with TLA+ and the TLC model checker.

What's verified (tla/RamDiskSystem.tla):

Property	Meaning
PoolConsistent	Pool accounting: rented <= allocated <= maxPages
NoPageLeak	Every rented page is accounted for (in a file or in-transit)
FreeBytesAccurate	FreeBytes = Capacity - RentedPages — never polluted by intermediate state
DataIntegrity	No file ever contains another file's data
ReadConsistent	Reads always return data belonging to the file being read
DeadFilesClean	Deleted files hold no pages
WriteTerminates	Every write eventually completes or fails (liveness)

Verified configurations:

Config	Pages	Files	Distinct States	Result
Minimal	3	2	3,163,692	All pass
Standard	4	2	66,190,728	All pass

The model covers: 3-phase write (scan/rent/assign), concurrent reads, sparse extend, truncate, delete, file creation, SetAllocationSize TOCTOU check, and GetVolumeInfo as an external observer.

Historical context: An earlier narrow model (PagePoolFixed.tla) only verified the PagePool reserve/rent protocol. It missed a system-level bug where Reserve() in SetLength polluted FreeBytes, causing stale metadata under high concurrency. The full-system model (RamDiskSystem.tla) was built to prevent such gaps.

Building from Source

Requires .NET 10 SDK and WinFsp 2.x (install with Developer files).

# Regular build
dotnet build

# AOT publish (requires Visual Studio C++ Build Tools)
dotnet publish src/RamDrive.Cli/RamDrive.Cli.csproj -c Release -r win-x64 -o ./publish-aot

Release

Push a tag matching release-X.Y.Z to trigger the CI pipeline, which builds, tests, and creates a GitHub Release with the AOT-compiled binary.

License

MIT

This project uses WinFsp - Windows File System Proxy, Copyright (C) Bill Zissimopoulos, under the GPLv3 with FLOSS exception.