btrfs send slow / how to improve performance

Hi,

i was trying to clone / copy a 4TB Raid 50 Array (mdadm) using btrfs send.

But btrfs send is sending with just 2MB/s. Is there any way to speed up btrfs send?

There's nearly no I/O while running btrfs send but 100% CPU Load of the btrfs command.

Kernel: 3.18.12
btrfs progs: 3.19.1

Greets,
Stefan