If you need to test actual internet download speeds rather than local disk performance, several specialized servers host large files for public use: Quickly create a large file on a Mac OS X system?
For high-speed connections, a 50 GB file provides enough duration to observe network stability and thermal throttling over several minutes. 50 gb test file
Linux users can use the fallocate command, which is the most efficient way to pre-allocate space. fallocate -l 50G testfile.img If you need to test actual internet download
Modern drives often have "burst speeds" thanks to SLC caching. A small file might fit entirely in this fast cache, giving a false impression of performance. A 50 GB file forces the drive to reveal its true, sustained write speed. fallocate -l 50G testfile
Windows users can use the fsutil tool. You must run the Command Prompt as an . Command: fsutil file createnew testfile.dat 53687091200