How to Generate File of a determinate Size in Windows?

Question

How is the Best and fastest way to do it?

Solution 1

I found this Page, I try it and work great.

To create a single File use

fsutil file createnew filename filesize

To create a lot of Files use

For /L %i in (1,1,25000) do fsutil file createnew A%i.tmp 12288

will create 25,000 files of 12288 bytes (12KB) named A1.tmp, A2.tmp, A3,tmp…

Solution 2

PowerShell:

$f = new-object System.IO.FileStream c:\temp\test.dat, Create, ReadWrite
$f.SetLength(42MB)
$f.Close()

This will create a file c:\temp\test.dat that consists of 42MB of nullbytes. You can of course just give byte count instead as well. (42MB = 42 * 1048576 for PowerShell).

Note:
Keep in mind that unless you specify the full path (in my example, C:\temp\test.dat), using relative paths (i.e .\test.dat) will only create files on the directory where PS was started in, i.e. ["C:\users\currentUser"] if you start PS from the Run... command, or ["C:\Windows\system32"] if you start it with Shift+RightClick (OR) Alt->F>S>R on the windows explorer.
To workaround this, you must change the underlying directory (you can check it with this as a command on PS: [IO.directory]::GetCurrentDirectory()) to the current path you're on in the PS console, simply including the line:

[IO.directory]::SetCurrentDirectory($(get-location).Path)

So, to wrap it up, you make it work with the relative path you're currently in:

[IO.directory]::setCurrentDirectory($(get-location).Path) #Changes directory to current PS directory
[Int64]$size = 150MB #This allows you to set the size beforehand
$f = new-object System.IO.FileStream .\test.dat, Create, ReadWrite
$f.SetLength($size)
$f.Close()

Solution 3

c:\>fsutil file createnew /?
Usage : fsutil file createnew <filename> <length>
   Eg : fsutil file createnew C:\testfile.txt 1000

Comments

[ICTMitchell]

What language/environment in Windows? cmd-files? Powershell? C#?

[ZXX]

Beware that this only generates so called sparse file - you get a record in a folder with a file size but not actual data clusters assigned with the file. So for purposes like testing, zeroing or blocking off large blocks of data clusters it's useless.

[Anders]

I might add that this is extremely fast to do.

[mklement0]

@ZXX: I don't think that fsutile file createnew <file> <size> creates sparse files - the docs make no mention of that, and running fsutil sparse queryflag <file> on a file created this way indeed suggests that the file is not sparse.

[sawyer seguin]

@msanford In fact, you can use relative paths, but they will be relative to the directory PowerShell was started in (i.e. [IO.Directory]::GetCurrentDirectory()), and not relative to the directory you switched to using the cd or Set-Location command.

[sawyer seguin]

Which is generally true for any kind of COM or .NET interop you perform inside PowerShell.

[msanford]

@mihi Thank you for that additional details; I assumed it was something of this nature! So, for those getting New-Object : Exception calling ".ctor" with "3" argument(s): "Could not find a part of the path c:\some\path\test.dat` see above :)

[thatOneGuy]

@Anders unbelievably fast