iSCSI issues after upgrading to 11.2 x64 RELEASE

Tue Sep 4 16:57:04 UTC 2018

> The NIC's are Intel based using igb kernel driver:
> 
> igb0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 9000
> options=6403bb<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_HWCSUM,TSO4,TSO6,VLAN_HWTSO,RXCSUM_IPV6,TXCSUM_IPV6>

I see your MTU is 9000, and as described by the other thread you linked to, there are issues with 9k jumbo cluster allocation.
Some detailed notes are here, but the quick summary is: set MTU < 4096
https://gist.github.com/freqlabs/eba9b755f17a223260246becfbb150a1

> Can anyone suggest anything to stop my system from completely locking up and becoming unresponsive?
> At the moment I'm not sure if switching to 'Stable' or 'Current' branches is a good solution?

The problem has been mitigated for a while on 12-CURRENT, so that might be worth trying. Otherwise I’ve been hoping a committer will put this fix in 11-STABLE, but in the meantime you could manually apply the patch:
https://reviews.freebsd.org/D16534 <https://reviews.freebsd.org/D16534>

- Ryan