Quickly create large file on a Windows system

fsutil file createnew <filename> <length>

where <length> is in bytes.

For example, to create a 1MB (Windows MB or MiB) file named 'test', this code can be used.

fsutil file createnew test 1048576

fsutil requires administrative privileges though.

You can use the Sysinternals Contig tool. It has a -n switch which creates a new file of a given size. Unlike fsutil, it doesn't require administrative privileges.

Check out RDFC http://www.bertel.de/software/rdfc/index-en.html

RDFC is probably not the fastest, but it does allocate data blocks. The absolutely fastest would have to use lower level API to just obtain cluster chains and put them into MFT without writing data.

Beware that there's no silver bullet here - if "creation" returns instantly that means you got a sparse file which just fakes a large file, but you won't get data blocks/chains till you write into it. If you just read is you'd get very fast zeros which could make you believe that your drive all of the sudden got blazingly fast :-)

Check the Windows Server 2003 Resource Kit Tools. There is a utility called Creatfil.

 CREATFIL.EXE
 -? : This message
 -FileName -- name of the new file
 -FileSize -- size of file in KBytes, default is 1024 KBytes

It is the similar to mkfile on Solaris.

Short of writing a full application, us Python guys can achieve files of any size with four lines, same snippet on Windows and Linux (the os.stat() line is just a check):

>>> f = open('myfile.txt','w')
>>> f.seek(1024-1) # an example, pick any size
>>> f.write('\x00')
>>> f.close()
>>> os.stat('myfile.txt').st_size
1024L
>>>

Use:

/*
Creates an empty file, which can take all of the disk
space. Just specify the desired file size on the
command line.
*/

#include <windows.h>
#include <stdlib.h>

int main (int argc, char* ARGV[])
{
    int size;
    size = atoi(ARGV[1]);
    const char* full = "fulldisk.dsk";
    HANDLE hf = CreateFile(full,
                           GENERIC_WRITE,
                           0,
                           0,
                           CREATE_ALWAYS,
                           0,
                           0);
    SetFilePointer(hf, size, 0, FILE_BEGIN);
    SetEndOfFile(hf);
    CloseHandle(hf);
    return 0;
}

The simplest way I've found is this free utility: http://www.mynikko.com/dummy/

Creates dummy files of arbitrary size that are either filled with spaces or are filled with non-compressible content (your choice). Here's a screenshot:

I found a solution using DEBUG at http://www.scribd.com/doc/445750/Create-a-Huge-File, but I don't know an easy way to script it and it doesn't seem to be able to create files larger than 1 GB.

You can use the cat powershell command.

First create a simple text file with a few characters. The more initial chars you enter, the quicker it becomes larger. Let's call it out.txt. Then in Powershell:

cat out.txt >> out.txt

Wait as long as it's necessary to make the file big enough. Then hit ctrl-c to end it.

Quick to execute or quick to type on a keyboard? If you use Python on Windows, you can try this:

cmd /k py -3 -c "with open(r'C:\Users\LRiffel\BigFile.bin', 'wb') as file: file.truncate(5 * 1 << 30)"

Another GUI solution : WinHex.

“File” > “New” > “Desired file size” = [X]
“File” > “Save as” = [Name]

Contrary to some of the already proposed solutions, it actually writes the (empty) data on the device.

It also allows to fill the new file with a selectable pattern or random data :

“Edit” > “Fill file” (or “Fill block” if a block is selected)

I've made some additions to the same fsutil method as mentioned in the chosen answer. This is to create files of many different extensions and/or of various sizes.

set file_list=avi bmp doc docm docx eps gif jpeg jpg key m4v mov mp4 mpg msg nsf odt pdf png pps ppsx ppt pptx rar rtf tif tiff txt wmv xls xlsb xlsm xlsx xps zip 7z
set file_size= 1
for %%f in (%file_list%) do (
fsutil file createnew valid_%%f.%%f %file_size%
) > xxlogs.txt

The code can be cloned from https://github.com/iamakidilam/bulkFileCreater.git