[ILUG] Best BS value for dd

[O'Sullivan, Damian]

Hi,

I am doing a lot of disk cloning/erasing with dd. I was wondering how I
would find out the best value for bs so that it will run as fast as
possible. I understand there are probably a few factors such as
RAM,disks etc. 

Eg :

No compression :
dd if=/dev/hda of=/someotherdisk/image.bin bs=????

Compression

dd if=/dev/hda bs=???? | gzip | of=/someotherdisk/image.bin bs=????

Also if doing over a network it would be slower how do I factor that in?

dd if=/dev/cciss/c0d0 of=/tmp/SomeNfsMountedPlace/image.bin bs=????

Disk wiping :

dd if=/dev/zero of=/dev/hda bs=???


Thanks for any ideas. I guess there is no magic number but would like to
know how to come up with how to get a number depending on setup.

D.