write large file to disk

shag7 (3)

Hi,

I wrote a little c++-prog (for WinXP), that writes random data to my harddisk. I used ofstream, but the resulting transferrate is not what I expected (it´s too slow).

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	ofstream outfile( filename, ofstream::binary );
	for( int h = 0; h < blockcount; h++ ){
		outfile.write( buffer, BLOCKSIZE );
	}
	outfile.close();

Is there a faster way of writing large amounts of data? Is there some kind of "low level access" to IDE-disks? Is there a "ATA command programming guide"?

Thanks in advance!

Have a nice day
Sebastian

helios (829)

This belongs in General C++ Programming, but anyway: write() is actually pretty darn fast. You probably just made BLOCKSIZE too small. How large is it? 5 MB should give a decent rate, but of course, the bigger the block size, the more data can be transferred in a single loop cycle and function call, and the less overhead from these structures.

Last edited on

shag7 (3)

yes, I hoped there are "special windows functions" to perform this task. Thats why i placed it here

BLOCKSIZE was 10MB but transfer rate was ~ 0.3*MAXTRANSFERRATE and CPU usage was at 100%!

(MAXTRANSFERRATE = max hdd transferrate measured with h2benchw)

h2benchw writes to disks containing no partitions. I think I have to find out how this is done. Any hints? ;-)

greets and thanks
Sebastian

helios (829)

What?! Just how much data were you moving?
If you're just copying large amounts of data, don't load it to memory. You're just adding a middle man to the equation (disk->RAM->disk instead of disk->disk), which is why you'll never get 100% performance.
Let's see... I'm sure there must be some OS function for this...
Ah, here we go. CopyFile(): http://msdn.microsoft.com/en-us/library/aa363851(VS.85).aspx

shag7 (3)

Thanks a lot!

WriteFile and CopyFile were the functions I was looking for.

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