Create large files of random information

I wanted to test that mischevious hard drive, to avoid problems when I move stuff on to it.

The plan was to fill it with dummy files and if there was an issue at the 40Gb point, I would know up front. Which would have been better than finding out a week later.

To that end, the weak-sauce tip for the day becomes this one: Creating a series of 2Gb files made of random gibberish, just to take up space.

for i in {1..20} ; do time dd if=/dev/urandom of=test-{$i}.file bs=268435456 count=8 ; done

The results, after a considerable amount of time (/dev/zero is faster), will be twenty files all 2Gb in size, filled with gunk. Good gunk, that is.

A little tip there: The block size multiplied by the count gives you the size of the file. So what?

So simply setting the block size to one gigabyte (or gibibyte, since I seem to be drawing flak on the issue these days :) ) might cause memory errors on a machine with only 512Mb or less. It did for me.

The size of the file in my case wasn’t really important I guess, but I did get that quick primer for performing this stunt on low-memory machines. Reduce the block size, magnify the count, get the same results.

Oh, and the hard drive? It’s fine. I filled it all the way to the brim, and Arch didn’t complain. Good to know.

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5 Responses to “Create large files of random information”

  1. 1 jimmy 2011/04/01 at 6:23 AM

    Is there any particular reason you use random gibberish? I wanted to fill a disk the other day and simply used dd to create multiple files from /dev/zero.

    • 2 K.Mandla 2011/04/01 at 8:02 AM

      No real reason, I guess. At the time my fear was that only zeroes wouldn’t trigger an error, if there was some sort of limit to the drive. Now that seems silly though. :oops:

    • 3 iss 2011/04/11 at 2:13 AM

      Doesn’t filling files with zeros make them sparse? It would be pointless to test disk with sparse files.

  2. 4 Sassan 2011/04/14 at 12:05 AM

    It would probably be more appropriate to use a smaller block size and a larger count, since all the larger blocksize is achieving is wasting huge amounts of ram during the process.

  1. 1 A bash loop, for pacman « Motho ke motho ka botho Trackback on 2011/04/01 at 9:47 PM

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Some recent desktops

May 6, 2011
Musca 0.9.24 on Crux Linux
150Mhz Pentium 96Mb 8Gb CF

May 14, 2011
IceWM 1.2.37 and Arch Linux
L2300 core duo 3Gb 320Gb

Some recent games

Apr. 21, 2011
Oolite on Xubuntu 11.04
L2300 core duo 3Gb 320Gb

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