move disk to iscsi storage slow

hi,

i add a freenas iscsi storage to my proxmox.

now i want to move a disk from local (qcow2) to iscsi (raw). the disk is 20GB big.

2 Problems:

1. i think its realy slow (needs about one Hour) and i have a Gbit Network (tested with iperf, result: 936 Mbits/sec)

2. other system which have there disk on iscsi have extremly bad performance during the "movement"

what could be the reason?

thx!