why averaging only 4MB/s and how to spare bad blocks?

[sjs]

whats also interesting, is that when the disk image is mounted:

Finder > Get Info reveals: 7.71GB ( byte size notwithstanding)

and yet

$ dh -kh
$ 5.1G .

and well as:
$ ls -lh
-rwx------ 1 demo demo 5G Mar 21 01:06 demo.sparseimage

quite an unexpected difference to me. 2.6GB or 2.7GB less data then I thought I had. Quite amazing.

At first I thought 1/3 of my data was missing or SD failed, but thats not the case. Just a pleasant surprise.

Thinking about it now, I think this is probably due to the cluster size within the sparseimage, as I have tons of small text files in there. I wonder if I can make the cluster size 1K or so on a sparse image.

Either way this make SD a great way to copy filevaults for me.

I would have to suspect, however, that the SD benefit is only the 1st time. If I keep doing a Smart Update, I'd guess I'd quickly fragment up and grow this image too. I'd imagine that even an "Erase, then Copy Files" would not shrink the sparse image would it? I'd imagine even if you did a format to the volume when you do your "Erase" (do you?) it would not shrink unless your Erase really deletes or compacts the image (not a bad idea if you dont)...
Just some thoughts...