About dd command

Shell Programming and Scripting
1

Hi folks,

How to find the value of bs= to have the best performance of dd in cloning disk image? TIA

B.R.
satimis

2

hi,
it converts and copies file.

e.g.
dd if=/dev/cdrom of=image.iso bs=2k

it creats disk image from CD rom.

if size is of unknown length we can use CP command or else dd for best perfomance.

3

Hi subhendu81,

Thanks for your advice.

On a Virtual Machine running Xen, I run following dd command to clone an image;

# dd if=/path/to/disk.img of=/new_path/to/disk.img bs=4k

It works. But I expect to find out bs=? would have the best result running the above command.

B.R.
satimis

4

There was a thread about optimizing block size a few months ago, but I think the simple answer is "measure it". Do a quick copy of a sizable chunk of data with different block sizes and examine the throughput rate -- my version of dd helpfully prints it when it finishes, so you don't even have to calculate it. Probably 4k is way too small on contemporary hardware.

http://www.unix.com/members-only/69299-optimum-blocksize-clone-disk.html is the old thread -- pretty much a must read for this question really!