[SunHELP] Gigabit Ethernet throughput

[DAUBIGNE Sebastien - BOR ( SDaubigne@bordeaux-bersol.sema.slb.com )]

We have 2 Solaris 2.6 Servers with a Gigabit Ethernet link (ge driver) and
we can't achieve the throughput we expected.

First we could not achieve more than 25 Mb/s on a single FTP transfer, so we
decided to lauch multiple FTP transfers.
The best we got was 46 Mb/s (aggregate) with 10  parallel FTP, which was
much better but not sufficient.

I found a document in Sunsolve which stated that increasing the TCP default
window size (8K) could speed up the throughput, so I ran theses two commands
to set it to the  16 bits TCP-window limit :

ndd -set /dev/tcp tcp_xmit_hiwat 65535
ndd -set /dev/tcp tcp_recv_hiwat 65535

After this we  reached 57 Mb/s aggregate.

Sun told us the maximum throughput should be 200 Gb/h, which is 57 Mb/s so
we are there.
I could hardly admit that the maximum throughput of a GE link is 57*8=456
Mbit/s.
On a FastEthernet link  (100 Mbits) we got 10 Mb/s, so assuming the same
ratio, I expect 800 Mbit/s (100 Mb/s).

So my first question is : What is the maximum thoughput of a GE link ?

Next, still on Sunsolve I found a document which talks about parameters to
enable TCP large windows (to use 32 bits TCP-windows and go beyond the 16
bits TCP windows limit).
After reading the related RFC (1323) I think I could release the 65535 limit
with theses params, to achieve 100 Mb/s thoughput.

So my second question is : Did anybody play with TCP large windows and these
related parameters :

tcp_wscale_always
tcp_tstamp_always
tcp_tstamp_if_wscale
tcp_xmit_hiwat > 64 K -1
tcp_recv_hiwat > 64 K -1

What are the best window size for a GE link ?

---
Sebastien DAUBIGNE 
sdaubigne at bordeaux-bersol.sema.slb.com <mailto:sebastien.daubigne at sema.fr>
- (+33)5.57.26.56.36
SchlumbergerSema - SGS/DWH/Pessac