Creating a test/junk file around 2gb

jeriryan · 06-10-2008, 12:09 PM

I need to create a test/junk file to benchmark the performance of a tape drive, but apparently I didn't install mkfile by default so is there any alternative? (Assume that even though I'm asking this question on the internet, I can't access the internet on Red Hat, so I'd like a built-in solution.)

pwc101 · 06-10-2008, 12:15 PM

Code:

dd if=/dev/zero of=./test_file bs=1024 count=2000000

ischi · 06-10-2008, 08:30 PM

for a benchmark file it might be better to use /dev/random as a source just to get around any optimization that might be happening through compression while trenfering the file (just a thought dont know what you wnat to do excatly)

Code:

dd if=/dev/random of=./test bs=1024 count=2000000

pwc101 · 06-11-2008, 04:58 AM

Quote:

Originally Posted by ischi

for a benchmark file it might be better to use /dev/random as a source just to get around any optimization that might be happening through compression while trenfering the file (just a thought dont know what you wnat to do excatly)

Code:

dd if=/dev/random of=./test bs=1024 count=2000000

Using /dev/random to create a 2GB file would take a year! /dev/random uses mouse input etc. as input to generate random numbers, and thus doesn't contain much data. It would be better to use /dev/urandom, which generates pseudo random data. However, this would still take a lot longer as generating the pseudo random data is processor intensive.

syg00 · 06-11-2008, 05:21 AM

Mmmm - all random number generators need seeding. That's not the problem with /dev/random, but the fact that it blocks. /dev/urandom is a indeed better option, since it doesn't block - *if* the data really needs to be random.

Of more concern when I have done this sort of thing is whether the data needs to be a of a particular structure - say 20 chars followed by 8 digits, followed by ...
I tend to generate a small file, then copy (append) the file back and forth; fibonacci growth, and quickly gets to the required size. Simple shell script handles things.