topic Re: mtu size to be increased in alpha openvms v7.3-2 in Operating System - OpenVMS

mtu size to be increased in alpha openvms v7.3-2

kirit_2 — Wed, 02 Feb 2005 02:56:36 GMT

Hi

I want ot increase mtu size in gigabit interface of alpha openvms systems. reason to change it I am getting very low throughput while connecting two alpha systems back to back with 1000baseSX card and do ftp - its just 4.6 Mbps,
default mtu is 1500 , I want to change it to 9000.

please help me how to do and what could be the reason for getting such a low throughput.

Thanks in advance.

regards

Kirit

Re: mtu size to be increased in alpha openvms v7.3-2

David B Sneddon — Wed, 02 Feb 2005 03:05:51 GMT

Kirit,

Not sure if this will help since I don't use any
gigabit links...

$ MCR LANCP SET DEVICE device/JUMBO

will set the device for jumbo packets (which is
what I assume you are after).

$ MCR LANCP HELP SET DEVICE will give you other
options.

Regards
Dave

Re: mtu size to be increased in alpha openvms v7.3-2

Kris Clippeleyr — Wed, 02 Feb 2005 03:27:26 GMT

Kirit,

Did you verify the speed settings in LANCP?
$ MC LANCP SHOW DEVICE ewa0 /CHAR
Note that SET DEVICE/SPEED changes only the volatile database, use the /PERMANENT qualifier.
If you have the chance, also verify the settings at console level.
>>> SHOW EWA0_MODE (or equivalent)
Regards,
Kris (aka Qkcl)

Re: mtu size to be increased in alpha openvms v7.3-2

Ian Miller. — Wed, 02 Feb 2005 04:43:17 GMT

Kirit, see
http://h71000.www7.hp.com/doc/732final/6631/6631pro_006.html#gbe_perf
for details on the various steps required.

Re: mtu size to be increased in alpha openvms v7.3-2

Jiri Zelenka — Thu, 03 Feb 2005 02:31:38 GMT

Hi Kirit,

the ftp is not the best way to find out a raw throughput of a lan card. If you do that, be sure to use a null device as destination. Or use a TTCP tool.

Jiri

Re: mtu size to be increased in alpha openvms v7.3-2

Cass Witkowski — Fri, 04 Feb 2005 18:04:11 GMT

I think there is a SYSGen parameter called LAN_FLAGS that may need to be set for jumbo frames.

Be aware that some older CISCO switches while they support Gigabit Ethernet do not support jumbo frames. We found this out when we upgraded OpenVMS and as soon as we started using jumbo frames the switch went out to lunch

Re: mtu size to be increased in alpha openvms v7.3-2

Hein van den Heuvel — Fri, 04 Feb 2005 22:19:05 GMT

>>> back to back with 1000baseSX card and do ftp - its just 4.6 Mbps,

Is that Mega BYTE per sec or BITS?

Even if it is Megabytes, it still is only 50
Mbits/sec and thus a magnitude too slow.
A bigger packet size is not going to solve that. Something else is wrong.
As others wrote ftp is not your best test.. it may well be limited by write speed.
What are you going to use the Gigabit connection for. Can you use that as the test tool also? If you are going to use it just for ftp, then ftp is of course the right test.
Is the negotiated speed indeed 1000?

Good luck,
Hein.

Re: mtu size to be increased in alpha openvms v7.3-2

Eric Dittman — Tue, 08 Feb 2005 12:13:39 GMT

What is the configuration of you network? Are the GigE interfaces directly connected or are they going through a switch? If they are on a switch, what model switch are you using and what else is connected?

Re: mtu size to be increased in alpha openvms v7.3-2

Ian Miller. — Tue, 08 Feb 2005 18:02:11 GMT

Cass, read the link I posted above, LAN_FLAGS is one of the things that have tobe set.