Quickly create large file on a Windows system

Question

In the same vein as Quickly create a large file on a Linux system   I d like to quickly create a large file on a Windows system  By large I m thinking 5 nbsp GB  The content doesn t matter  A built-in command or short batch file would be preferable  but I ll accept an application if there are no other easy ways

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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     gt  xxlogs txt   The code can be cloned from https   github com iamakidilam bulkFileCreater git

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Use      Creates an empty file  which can take all of the disk space  Just specify the desired file size on the command line       include  lt windows h gt   include  lt stdlib h gt   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

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Open up Windows Task Manager  find the biggest process you have running right click  and click on Create dump file   This will create a file relative to the size of the process in memory in your temporary folder   You can easily create a file sized in gigabytes

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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

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Simple answer in Python  If you need to create a large real text file I just used a simple while loop and was able to create a 5 nbsp GB file in about 20 seconds  I know it s crude  but it is fast enough   outfile   open  outfile log    a     def write outfile       outfile write  hello world hello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello worldhello world    n       return  i 0 while i  lt  1000000      write outfile      i    1 outfile close

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I was searching for a way to generate large files with data  not just sparse file  Came across the below technique      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      gt  dummy txt for  L  i in  1 1 14  do type dummy txt  gt  gt  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

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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  gt  gt  out txt   Wait as long as it s necessary to make the file big enough  Then hit ctrl-c to end it

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PowerShell one-liner to create a file in C  Temp to fill disk C  leaving only 10 nbsp MB    io file   Create  C  temp bigblob txt   SetLength  gwmi Win32 LogicalDisk -Filter  DeviceID  C     FreeSpace - 10MB  Close

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I found an excellent utility that is configurable at https   github com acch genfiles   It fills the target file with random data  so there are no problems with sparse files  and for my purposes  testing compression algorithms  it gives a nice level of white noise

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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

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fsutil file createnew  lt filename gt   lt length gt   where  lt length gt  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

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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     gt  gt  gt  f   open  myfile txt   w    gt  gt  gt  f seek 1024-1    an example  pick any size  gt  gt  gt  f write   x00    gt  gt  gt  f close    gt  gt  gt  os stat  myfile txt   st size 1024L  gt  gt  gt

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Temp files should be stored in the Windows Temp Folder  Based on the answer from Rod you can use the following one liner to create a 5 GB temp file which returns the filename   System IO Path   GetTempFileName          System IO File   Create     SetLength 5gb  Close                   Explanation     System IO Path   GetTempFileName   generates a random filename with random extension in the Windows Temp Folder The Pipeline is used to pass the name to  System IO File   Create     which creates the file The file name is set to the newly created file with  SetLength 5gb   I was a bit surprised to discover  that PowerShell supports Byte Conversion  which is really helpful  The file handle needs to be closed with  close to allow other applications to access it With     the filename is returned and with            it is ensured that only the filename is returned and not the empty string returned by  System IO File   Create

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You can try this C   code    include lt stdlib h gt   include lt iostream gt   include lt conio h gt   include lt fstream gt   using namespace std   int main         int a      ofstream fcout   big file txt        for   a    1999999999           do              fcout  lt  lt  a                    while  a             Maybe it will take some time to generate depending on your CPU speed

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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  -

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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

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Plain ol  C     this builds under MinGW GCC on Windows XX and should work on any  generic  C platform   It generates a null file of a specified size  The resultant file is NOT just a directory space-occupier entry  and in fact occupies the specified number of bytes  This is fast because no actual writes occur except for the byte written before close   My instance produces a file full of zeros - this could vary by platform  this program essentially sets up the directory structure for whatever data is hanging around    include  lt stdio h gt   include  lt stdlib h gt   FILE  file   int main int argc  char   argv        unsigned long  size       if argc  3                printf  Error     syntax  Fillerfile  size  Fname  n n            exit 1              size   atoi  amp  argv 1         printf  Creating  d byte file   s     n   size   amp  argv 2         if   file   fopen  amp  argv 2    w                    printf  Error opening file  s  n n    amp  argv 2            exit 1              fseek file  size-1  SEEK SET       fprintf file    c   0x00       fclose file

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I was looking for a way to create a large dummy file with space allocation recently  All of the solutions look awkward  Finally I just started the DISKPART utility in Windows  embedded since Windows Vista    DISKPART CREATE VDISK FILE  C  test vhd  MAXIMUM 20000 TYPE FIXED   Where MAXIMUM is the resulting file size  20 GB here

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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

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Another GUI solution   WinHex      File     gt     New     gt     Desired file size       X     File     gt     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     gt     Fill file     or    Fill block    if a block is selected

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1 MB file dummy txt within few seconds    echo  This is just a sample line appended to create a big file      gt  dummy txt for  L  i in  1 1 14  do type dummy txt  gt  gt  dummy txt   See here   http   www windows-commandline com how-to-create-large-dummy-file

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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  lt  lt  30

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I needed a regular 10 GB file for testing  so I couldn t use fsutil because it creates sparse files  thanks  ZXX     echo off     Create file with 2 bytes echo  gt file-big txt     Expand to 1 KB for  L   i in  1  1  9  do type file-big txt gt  gt file-big txt     Expand to 1 MB for  L   i in  1  1  10  do type file-big txt gt  gt file-big txt     Expand to 1 GB for  L   i in  1  1  10  do type file-big txt gt  gt file-big txt     Expand to 4 GB del file-4gb txt for  L   i in  1  1  4  do type file-big txt gt  gt file-4gb txt  del file-big txt   I wanted to create a 10 GB file  but for some reason it only showed up as 4 GB  so I wanted to be safe and stopped at 4 GB  If you really want to be sure your file will be handled properly by the operating system and other applications  stop expanding it at 1 GB

[windows] Quickly create large file on a Windows system

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