I keep reading conflicting things about this topic.
I wanted to make a dban disk wiping floppy. Some
people say use:

others say

or even:

I would think the latter two would be much faster
because the 512 bytes would need about 2800
write events to do the whole 1.44 megs
but doing it in 18k or 1440 chunks would be faster.
But someone said that if the bs is too big
there might be a problem if the image is
really crammed to fit the floppy, you might lose
that last part? The reason I was wanting to not
use 512 is the drive seems to take forever using
it that way. If the exact byte size of the image
is:

could I do this:

just write the whole thing in one big stream?

Mark

from 'How to ask questions the smart way' (www.catb.org/~esr/faqs/smart-questions.html):

"Try it and see. If you did that, you'd learn the answer."

Seriously. Try it, see if it works. If it doesn't, create the floppy in some other way.

What's fastest probably depends on a lot of factors, but I figure the time per write operation is affinely linear in the number of bytes; that is, the number of seconds per write is a*x + b for x bytes and some magic numbers a and b.

However, the kernel may muck with the writes, delaying them a bit to optimize it.

Bottom line: try a handful of bs/count combinations, see if they work, time them to see which is fastest. You'll probably see a pattern, so investigate that.

hth --Jonas

The smaller block size causes the floppy to get hit with many more
interrupts than the bigger size. I guess what I was asking was
whether there's a risk of bytes being lost if you use the
bigger bs. I also don't just want to experiment with it because
one of the image writes I wanted to do was for a DVD writer
firmware update, and in that case every single byte has to
be correct or my DVD could become a paperweight. I suppose
I could do the experiment and then mount the image file
via loopback and compare the two, that should be able to
confirm an exact copy.

yeah, that ought to work.

For the next time around, make sure to state the whole problem in the thread--if I had known that you weren't just backing up your porn movies, I might have offered a different answer.

Also, be aware that Linux might cache what it has written to the disk (I'm not sure), so if you want to be totally sure (but see also "Trusting Trust", and think about whether you trust your hardware), you might have to shoot that cache (I don't know how, or if it caches writes as reads--one good argument to not do that is that the write might have been unsuccessful... maybe?).