You can include a progress report and estimated size of your ZFS send stream during the transfer process.
To estimate the ZFS send stream size:
# zfs send -rnv pool/opt@snap1
sending from @ to pool/opt@snap1
sending from @ to pool/opt/vol1@snap1
estimated stream size: 10.1G
To monitor the stream size during transfer process:
# zfs send pool/opt@snap1 | pv | zfs recv tank/opt
8.58GB 0:02:37 [95.7MB/s]
This enhancement provides visibility into your ZFS send stream transfers so that you can improve planning and scheduling of replication operations.