curious about results

[Trevor Woerner]

Hi,

I recently did a small write-up of my experiences using bmaptool:
http://twoerner.blogspot.ca/2014/03/using-bmaptool-to-create-memory-card.html

To summarize:
1. start with a small image which has about 62MB of data inside an 80MB
image
2. dd'ing this to a 4GB microSD takes about 18 seconds
3. create a new image with the same ~60MB of data but this time put it
inside a 3.7GB image
4. dd'ing this 3.7GB image to a 4GB microSD takes about 50 minutes
5. use bmaptools to reduce the time it takes to put the image onto the
microSD card

The important thing to note is that when booted, both images contain the
exact same data. There is no functional difference between the two
images. The only difference is that the same files are packaged into one
small and one large image.

When I used bmaptools to write the large 3.7GB image to the 4GB microSD
card, it ended up taking roughly 14 minutes. While that is certainly an
improvement over the 50 minutes it took dd to do the same job, I was
rather surprised that it was considerably longer than the 18 seconds it
took to dd the small image.

If both images contain the same files (i.e. the large image has exactly
the same files, but just has more empty space) I'm surprised the time to
write the same data jumps from 18 seconds to 14 minutes.

Is it because the ext3 filesystem (on which these images are based)
is... messy? Is ext3 scattering the filesystem data everywhere, making
it harder to skip empty blocks?

I have attached the bmap files I obtained for both the large and small
images.

Best regards,
    Trevor
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