Yes. You must use the bs option. And you have to do some tests to obtain the best performance. Start with 256k, then 512k, probably, 512k is the largest block size. You could also try 1024k.
Do test of some data and take the time, for example:
time dd if=/dev/sda of=/dev/sdb bs=256k count=100
And compare them with different block sized.
Another thing to consider is that probably you could use another tool to "image" your disk, avoiding the copy of unused disk space.
Por que hacerlo dificil si es posible hacerlo facil? - Why do it the hard way, when you can do it the easy way?
bs, blocksize does improve or degrade performance in dd read/writes.
The value for best speed depends on the layout of the disk itself, which varies based on the OS and the size of the disk.
If you are using LVM, you can obtain information on this and set your size with pvdisplay data.
Now I've said it can improve performance, its not always necessarily going to be dramatic and therefore worth your time.
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