How fast is slimRAW?

CinemaDNG processing speed will be limited by one of three potential bottlenecks: input storage throughput, output storage throughput or available CPU power. Since slimRAW compression is highly optimized, CPU power is rarely an issue on a modern computer. In most offload situations the limiting factor is input drive throughput. In archiving tasks the limiting factor might be output storage throughput, particularly when outputting to a hard drive. If the limiting factor is input storage throughput, slimRAW will typically be as fast as copying the files. If the limiting factor is output storage throughput, slimRAW can be even faster than copying.

Since this is a question we get occasionally, here are some non-scientific benchmarks for reference. All tests are done on a 1283 frames long 4K uncompressed CinemaDNG sequence with a total size of 16.77GB. Compression speed is compared with copying. Copy operations are executed with command line copy tools, because these are easy to time unlike copies done through Windows Explorer or macOS Finder.


Table 1: Windows 10, Intel i7-4770 quad core, input: external Samsung T7 SSD over USB3.0, output: internal SSD SATA III.
Operation Transfer speed in MB/s Time in seconds Relative time vs. slimRAW
slimRAW, lossless 451 37.2 100%
xcopy 400 41.9 113%
robocopy 454 36.9 99%


Table 2: Windows 10, Intel i7-4770 quad core, input: internal SSD SATA III, output: internal SSD SATA III.
Operation Transfer speed in MB/s Time in seconds Relative time vs. slimRAW
slimRAW, lossless 521 32.2 100%
xcopy 511 32.8 102%
robocopy 518 32.4 101%


Table 3: macOS Sonoma, mini M2, input: external Samsung T7 SSD over USB3.1 Gen2, output: internal SSD PCIE.
Operation Transfer speed in MB/s Time in seconds Relative time vs. slimRAW
slimRAW, lossless 766 21.9 100%
cp 711 23.6 108%


Table 4: macOS Sonoma, mini M2, input: internal SSD PCIE, output: external Samsung T7 SSD over USB3.1 Gen2.
Operation Transfer speed in MB/s Time in seconds Relative time vs. slimRAW
slimRAW, lossless 927 18.1 100%
cp 432 38.8 214%

Tables notes:
  • All slimRAW tests are done with slimRAW version 1.10
  • slimRAW lossless compression is done with default settings: Maximum compression is off, Fastest compression is off
  • The Samsung T7 is exFAT formatted for compatibility with both Windows and macOS
  • Transfer speed is based on input data size, for slimRAW the output data size is obviously smaller
  • Time for the copy operations is measured with Measure-Command in PowerShell on Windows and time in terminal on macOS
  • robocopy is run multiple times with different multithreading settings (/MT:numthreads) and the best setting is recorded in the tables

A few things to note:

  • When operations are input storage throughput limited, as in Tables 1, 2 and 3, slimRAW compression and direct copy operations are all similar in execution speed.
  • There is a dramatic difference with output storage limited operations, as in Table 4. Since slimRAW reduces the output file size, it has an advantage in these cases and can significantly improve offload speed compared to copying.
  • The same storage device connected to a different controller may exhibit different throughput limits, as demonstrated by the Samsung T7 connected over USB 3.0 (also known as USB 3.1 Gen1) on the Windows PC and over USB 3.1 Gen2 on the Mac mini.