RE: FTP bottleneck

Well, you were saying you had GB (gigabyte) speed Ethernet while the
iSeries is Gb (gigabit).  GB would max out around 1000MB/s v. Gb at
around 100-120Mb/sec; an 8 to 10-fold difference in speed and
throughput.

I don't know about the SSAP max frame sizes, but I imagine if anything
you could set these on all related systems.  But as I noted you should
talk about the change to jumbo frames (that's the 'technical' term they
use for frame over something around 4Kb) with your networking people to
make sure the LAN gear supports it and your company accepts jumbo frames
as a standard.  FWIW we don't do jumbo frames here as most of our comm
goes to the Internet which doesn't use it (at least not at the
endpoints).  Another FWIW you can mix and match jumbo & normal 1496
frames but the switches have to handle the packets and break them down
when going from jumbo to normal.

Your send/receive buffers are definitely too small.  You're shoving
multiple 600MB chunks through an 8KB buffer.  RAM allocated to these
buffers comes from the system (*MACHINE pool) and there is a point of
diminishing returns, but past articles I've read led me to use the 1MB
size here and it's working well for us.