Upgraded from 11.3-U4.1 to 12-RC1, and noticed that both iSCSI transfers and small file transfers via SMB took a huge hit in performance.
SMB for a 25GB photo archive I usually get 250MBps, and iSCSI I get 600MBps.
Large SMB transfers max out at 1GBps. Reads from iSCSI max out at 1GBps, writes at 25MBps.
I was using two laggs for mutlipath iSCSI, but have since removed them and tried assigning the IPs directly to the 10gb Chelsio interfaces. No change, even after reboot. No other configuration items like mtu set at all.
Removed IPs from Chelsio NICs, and re-assigned to the 1GB intel NICs. That drastically improved speeds for SMB and iSCSI, so to me it looks like maybe an issue with the Chelsio.