Linux ST (LTO tape driver) and iSCSI issue with large block sizes

Somewhere in the Linux SCSI subsystem and/or ST driver is an issue preventing block sizes > 1MB on tapes from working over iSCSI.

It is broken with both Linux as iSCSI server (initiator and target terminology hurt my brain) and using StarWind Tape Redirector on Windows as iSCSI server (someone else ran into the issue too).

The errors you might hit include:

st 8:0:0:0: [st0] Sense Key : Illegal Request [current] 
st 8:0:0:0: [st0] Add. Sense: Logical unit failure

[st0] Sense Key : Not Ready [current]
[st0] Add. Sense: Logical unit communication failure

dd: error reading '/dev/nst0': Input/output error

iScsiSptiDevice::scsiPassThrough: (SPTI) DeviceIoControl failed with error 87!

I gave up on trying to find the cause and instead found a viable alternative: rsh.

YMMV but my reason for using iSCSI is because I wanted full 1G ethernet speed. SSH sits at roughly half speed, and netcat at roughly 90% without tweaks, and involves a faff of commands on both ends.
RSH gives full 1Gbit/s speed with default settings, and is easy to use. Problem solved.