Question

I need to create a huge file filled with anything. I’m doing it this way but it takes so long:

exit 1 unless ARGV.length > 0
File.open("file-#{ARGV[0]}M.txt", 'w') do |f| 
  (ARGV[0].to_i*1048576).times {f.write(1) }
end

What’s the best way of doing that (in platform independent way?)

Answer 1

In *nix, use dd:

system("dd if=/dev/zero of=" + f + " bs=1 count=0 seek=" + ARGV[0] + "M");

If you want some content (instead of zeros) in the file, use

/dev/random

for if instead of /dev/zero

If you want a non-sparse file, use

bs=#{ARGV[0]}M

and omit seek

---

Universal method:

#Create a 1M fill buffer
fills = '1'*1048576
File.open("file-#{ARGV[0]}M.txt", 'w') do |f| 
  (ARGV[0].to_i).times {f.write(fills) }
end

It is similar to the one you have, but it writes 1M at a time. You write 1 byte at a time which creates a lot of overhead for hard disk to search and write. Writing 1M at a time will be much faster. If you have an even faster hard drive (like 16M/s), you can try to increase 1M to 16M.