How to create large dummy file

Fsutil.exe is a built in filesystem tool that is useful to do file system related operations from command line. We can create a file of required size using this tool.

syntax to create a file:

fsutil file createnew filename length
(length is in bytes)

For example, to create a dummy file test.txt, with size as 50MB :

fsutil file createnew test.txt 52428800

Note that the above command creates a sparse file which does not have any real data. If you want to create a file with real data then you can use the below command line script.

echo "This is just a sample line appended to create a big file.. " > dummy.txt
for /L %i in (1,1,14) do type dummy.txt >> dummy.txt

(Run the above two commands one after another or you can add them to a batch file.)

The above commands create a 1 MB file dummy.txt within few seconds.  If you want to create 1 GB file you need to change the second command as below.

echo "This is just a sample line appended to create a big file.. " > dummy.txt
for /L %i in (1,1,24) do type dummy.txt >> dummy.txt

Explanation:
The first command(echo…) creates the file dummy.txt with 64 bytes.
The second command, runs in a loop for 24 times, and each times doubles the size of the file, by appending it to itself.
One more example:

Create a 100MB file with real data:

echo "This is just a sample line appended  to create a big file. " > dummy.txt
for /L %i in (1,1,21) do type dummy.txt >> dummy.txt

The above command creates a 128 MB file.