Create Arbitrary Sized Sparse Files under Windows and Linux

Apparently there is something to be said about short blog posts. Allegedly I tend to get long winded sometimes and my posts can run a tad verbose sometimes. I usually tell people to STFU and go read Steve Yegge if they want to see verbose. I’m short, concise and to the point compared to him. But I figured that I’ll try some of that short blog post thing that people seem to be enjoying in other parts of the web. So I’m making a post about a silly little windows command. This is so that I don’t forget it about it next time I need it.

Have you ever needed a file of specific size to test something but you didn’t care what that file was? You know, just a space holder or a space filler kind of a thing? This is what you need to do to create one on Windows XP:

fsutil file createnew file.ext 10000

Naturally file.ext is the desired name of the file you want to create, and the numeric argument is the desired size in bytes. Note that fsutil creates a sparse file which means that this operation will be blindingly fast. For example it took about 3 seconds to create a 10GB file on my elderly windows machine.

Useful trick. I sometimes use it to see how a given app will act when it encounters a file of certain size. To accomplish the same thing in linux you apparently need to do something like:

dd if=/dev/zero of=my-file bs=1 count=0 seek=10G

I messed around with it, and the bs and count are important so don’t just skip them. The seek attribute specifies the desired size of your file, and here you can use human readable units (like 10Gb in the example).

So if you ever need a file of a specific size to test something, here is how you make one. How is that for a short post? What do you mean 350 words is not short? Ah, go to hell then. I tried. Next post will be verbose again. ;)