[colug-432] creating sparse disk images

Rick Hornsby richardjhornsby at gmail.com
Tue Nov 13 13:25:54 EST 2018

argh. sorry. Hit the wrong key combo before I was finished.

On November 13, 2018 at 11:13:31, Matthew Hyclak (hyclak at gmail.com) wrote:

Been a while since I did this, but I believe you have to make sure the
filesystem you want to be sparse actually contains 0's in the places you'd
like to be sparse before creating the sparse file.

 looks like a good starting point.

Thanks. I had seen that thread. I used zerofree, but it didn’t seem to
matter. Because of your link though, I read farther down the page to some
information about cp with the ‘—sparse=always’ flag, and some hints about
reported size between ls and du.
Interestingly enough, I messed around and got the following:

cp —sparse=always 16GB_file sparse_file -> 3.7GB, as per du. ls still says
it’s 16GB.

Right. So 16GB file drops to 3.7GB, says du.

I then copied (cp) that 3.7GB file back to my Mac without really thinking
too much and without any flags, and it ballooned into an 8GB file. No idea

I tried the same copy of the 3.7GB file again (Linux VM -> Mac with cp)
adding the —sparse=always flag this time, and it landed as a 4GB file. I
think maybe I’m on the right track, or at least getting there. Maybe.
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