Benchmark numbers for Dev Drive prerelease in Win11 22H2 Developer channel around the time of Dev Drive announce at Microsoft Build, May 2023.
Machine was a physical 8/16-core with NVMe. Disable Write Cache Flush flag = Disabled (OS default). All copies done on files with size set via file extents (no data written).
CoW links on Dev Drive take approximately constant time except at large file sizes. The savings is proportional to the file size, with 16MB files at about 31X performance, 1MB at 5.9X, and small sizes at about 2X. Note that all performance numbers are significantly better than the no-VHD 22H2 measurements in Win11 22H2 ReFS, reflecting the Windows Filesystem team's work to reduce overhead for Dev Drive.
| Method | FileSize | Mean | Error | StdDev | Median | Ratio | RatioSD |
|---|---|---|---|---|---|---|---|
| File.Copy | 0 | 136.0 us | 3.95 us | 11.57 us | 135.5 us | 1.00 | 0.00 |
| CoW | 0 | 102.9 us | 2.82 us | 8.17 us | 102.3 us | 0.76 | 0.08 |
| File.Copy | 1 | 305.4 us | 7.50 us | 21.26 us | 305.4 us | 1.00 | 0.00 |
| CoW | 1 | 130.6 us | 3.96 us | 11.16 us | 129.5 us | 0.43 | 0.05 |
| File.Copy | 1024 | 301.9 us | 6.77 us | 18.98 us | 301.7 us | 1.00 | 0.00 |
| CoW | 1024 | 133.6 us | 3.94 us | 11.49 us | 132.0 us | 0.44 | 0.04 |
| File.Copy | 16384 | 274.5 us | 6.35 us | 17.92 us | 272.4 us | 1.00 | 0.00 |
| CoW | 16384 | 132.1 us | 3.69 us | 10.75 us | 132.4 us | 0.48 | 0.05 |
| File.Copy | 262144 | 409.9 us | 8.53 us | 24.34 us | 408.0 us | 1.00 | 0.00 |
| CoW | 262144 | 134.3 us | 5.48 us | 15.74 us | 131.4 us | 0.33 | 0.04 |
| File.Copy | 1048576 | 774.4 us | 22.11 us | 65.20 us | 757.9 us | 1.00 | 0.00 |
| CoW | 1048576 | 132.7 us | 2.62 us | 6.53 us | 131.2 us | 0.18 | 0.01 |
| File.Copy | 16777216 | 6,571.5 us | 131.19 us | 239.89 us | 6,520.5 us | 1.00 | 0.00 |
| CoW | 16777216 | 210.3 us | 5.32 us | 15.34 us | 205.2 us | 0.03 | 0.00 |