Jumbo frame size variations

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Quattro Pete

Quattro Pete

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My NAS (Buffalo Linkstation) gives me the following options:
4102 bytes
7422 bytes
9694 bytes


The NIC in my PC gives me the following options:
2KB MTU
3KB MTU
4KB MTU
5KB MTU
6KB MTU
7KB MTU
8KB MTU
9KB MTU

My Rosewill switch's documentation just says 12 KB.


So, is this just going to be a trial end error type exercise in my case to see which of these values will actually work? Or can i assume that 9694 bytes on the NAS is equivalent to 9KB MTU on the PC and that the switch will accept and process any frame size that isn't larger than 12KB?
 
A bit OT, but

http://lwn.net/Articles/92727/

Quote:

The details are still being figured out, but it would appear that some routers on the net are rewriting the window scale TCP option on SYN packets as they pass through. In particular, they seem to be setting the scale factor to zero, but leaving the option in place. The receiving side sees the option, and responds with a window scale factor of its own. At this point, the initiating system believes that its scale factor has been accepted, and scales its windows accordingly. The other end, however, believes that the scale factor is zero. The result is a misunderstanding over the real size of the receive window, with the system behind the firewall believing it to be much smaller than it really is. If the expected scale factor (and thus the discrepancy) is large, the result is, at best, very slow communication. In many cases, the small window can cause no packets to be transmitted at all, breaking TCP between the two affected systems entirely.


I debugged a mail issue for three straight days until coming upon this gem. By shutting off scaling, mail started to flow. The "consumer grade" mail/virus/firewall/router/lawn-mower/water purifier installed at the other end advertised scaling, but didn't do it.

This was a few years ago, perhaps consumer grade stuff has improved, but don't be surprised if some connections don't work.
 
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Well, I experimented with jumbo frames a little yesterday... the gains were so small, it's really not worth the trouble of me getting a new main switch that supports jumbo frames. The weak link is my NAS... even with jumbo frames, it can only transfer about 12-13 MB/s. Without jumbo frames - around 10.5-11 MB/s.
 
Originally Posted By: Quattro Pete
Well, I experimented with jumbo frames a little yesterday... the gains were so small, it's really not worth the trouble of me getting a new main switch that supports jumbo frames. The weak link is my NAS... even with jumbo frames, it can only transfer about 12-13 MB/s. Without jumbo frames - around 10.5-11 MB/s.

You are probably more limited by the throughput of the hard drive.
 
Originally Posted By: tmorris1
Originally Posted By: Quattro Pete
Well, I experimented with jumbo frames a little yesterday... the gains were so small, it's really not worth the trouble of me getting a new main switch that supports jumbo frames. The weak link is my NAS... even with jumbo frames, it can only transfer about 12-13 MB/s. Without jumbo frames - around 10.5-11 MB/s.

You are probably more limited by the throughput of the hard drive.


If the drive is only capable of 10-12MB/sec, it has other issues, LOL.
 
Originally Posted By: Quattro Pete
Well, I experimented with jumbo frames a little yesterday... the gains were so small, it's really not worth the trouble of me getting a new main switch that supports jumbo frames. The weak link is my NAS... even with jumbo frames, it can only transfer about 12-13 MB/s. Without jumbo frames - around 10.5-11 MB/s.


This is a gigabit switch?
 
Originally Posted By: OVERK1LL
Originally Posted By: Quattro Pete
Well, I experimented with jumbo frames a little yesterday... the gains were so small, it's really not worth the trouble of me getting a new main switch that supports jumbo frames. The weak link is my NAS... even with jumbo frames, it can only transfer about 12-13 MB/s. Without jumbo frames - around 10.5-11 MB/s.


This is a gigabit switch?

Yes... and I do get about 85 MB/s between PCs. The problem is with this particular NAS.. it has a weak CPU, and despite having a gigabit NIC, it can't process frames fast enough.
 
Originally Posted By: tmorris1

You are probably more limited by the throughput of the hard drive.

I seriously doubt it.
 
Originally Posted By: Quattro Pete
Originally Posted By: OVERK1LL
Originally Posted By: Quattro Pete
Well, I experimented with jumbo frames a little yesterday... the gains were so small, it's really not worth the trouble of me getting a new main switch that supports jumbo frames. The weak link is my NAS... even with jumbo frames, it can only transfer about 12-13 MB/s. Without jumbo frames - around 10.5-11 MB/s.


This is a gigabit switch?

Yes... and I do get about 85 MB/s between PCs. The problem is with this particular NAS.. it has a weak CPU, and despite having a gigabit NIC, it can't process frames fast enough.


Are you sure it is linked at gigabit? The speeds you are getting are about the ceiling for 100Mbit.........
 
Originally Posted By: OVERK1LL

Are you sure it is linked at gigabit? The speeds you are getting are about the ceiling for 100Mbit.........

The port on the switch lights up as 1 Gbps when I connect it.

Spec sheet says so, too (HS-DH500GL):
http://www.buffalotech.com/files/products/LinkStation-Live_DS.pdf

It cost me about $80 shipped to my door about 2 years ago. You can't expect a whole lot at that price point. I only store music on it anyway, so those speeds are plenty fast for streaming.

By comparison, their 100Mbit NAS that I owned previously was only good for about 5 MB/s actual transfer speed.
 
LinkStation_Network.png
 
a bit off topic here...

Originally Posted By: Quattro Pete


By comparison, their 100Mbit NAS that I owned previously was only good for about 5 MB/s actual transfer speed.


In my testing here with the Drobo Pro, Drobo standard, Netgear ReadyNAS 3200 and some home-grown products, my tests echo your findings....

The Drobos we tested are nice, but can't maintain 1GB speeds at all. I sent them back. For nearly $3K, we need something that works quickly, not kinda quickly.

Bottom line from my testing: if a NAS is using an Intel Atom or other ultra-low power CPU, you will not see 1GB no matter how hard you try. If a device is using a real CPU, such as the QNAP TS-809 or NetGear ReadyNAS 3200/4200, both of these units use Intel Core2 CPUs, you'll see 1GB (or more) all day long.

Consumer-grade 100Mbit NAS proably won't see 100Mbit speeds either, as you have found.
 
Yup. Even a $300 Netgear NAS from Newegg only promises speeds of up to 25 MB/s. It uses IT3107 cpu.

If you want something that'll promise up to 100 MB/s, it'll cost $1K (Netgear ReadyNAS Pro - does not say what CPU it uses though).
 
I'll be bringing in a Patriot NAS here shortly to chuck a couple 1TB WD Green's into (cheap backup solution for a client). I'll bench it and see what it will do. This will be to my Intel Gigabit PCI-E NIC in my desktop through a Cisco 2960.
 
Here's the web interface for my 2960:

switch2.jpg


I'll be monitoring the transfer for the NAS when I test it using this. Will be interesting to see if it is CPU limited or if we start getting errors on the port..... Due to a junky NIC chipset.
 
Originally Posted By: Quattro Pete
Nice GUI!


Yeah, the Cisco web interface for their switches is quite nice. There is also software, like CNA that works well for this purpose too.
 
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