RT-AC66 with Jumbo frames on increase Tranfer rates through media bridge ?? HUH ??

[dolftb]

Hi

I am currently running 374.33 Beta 6. I just bought a Synology NAS DS213j and came across this phenomenon:

On the RT-AC66U I ticked "Jumbo Frames" but left the MTU size at default.
Sending large video files from NAS (Jumbo frames DISABLED) through AC-RT66U to media bridge (another RT-AC66U ) I noticed that the PC on the media bridge side was receiving 10-15mb/s more than with the Jumbo frames off. I tried this 3 times switching back and forth to Jumbo frames enabled and not, but was able to reproduce this speed increase every time over the media bridge.

Then I thought well sheesh I will turn on Jumbo frames on the end PC also! Well that didn't work out well at all as I could no longer access the NAS from behind the media bridge. Then I enabled jumbo frames on the NAS also and this lead to enormous decreases in transfers rates on the non media bridge side and still no connection to NAS through media bridge.

So currently this is what seems to work best with regards to transfer rates of large video files to and from NAS with Router setting Jumbo Frames option ticked on, are these stings:

- RT-AC66U jumbo frames enabled at 1500 MTU (haven't tried higher yet)
- All PC'S In front of media bridge and behind Jumbo frames off.
- NAS Jumbo Frames off
- All PC's Lan Hardwired
- Set 5GHZ to channel 40 (lost a few mb/s over other channels but gained persistent throughput


Large Video Average sustained transfer rates currently to and from NAS attached to main router:

- From behind media brigde (AMD A6 notebook with SSD 50mb/s download and 46mb/s upload
- On Router side From PC 1 (Intel I3 with SSD) to NAS 62mb/s Upload and 51MB/S download
- on Router side From Pc 2 ( I7 with ssd ) to Nas more or less same result as PC with I3

From PC1 to PC2 on RT-7 gig video file transfers at 91 MB/s yeah baby !!

Transfers from Notebook behind Media bridge to Computers on Main router only 25 mb/sec while to the NAs around 50mb/sec. What ?? Don't get this at all.....

Comments or advice anyone anyone ??

Thanks
Dolf

 

[PrivateJoker]

IMHO jumbo frames is only a (potential) advantage if all your machines are hardwired to a switch and your primary network activity is moving very large files across computers/file servers. Mixing standard (MTU 1500) and jumbo frames (usually defined as 9000, but I have devices that top out at 7000, and in real world testing on large files some people get best results from 4000) has the inevitable outcome of slowing performance. I also have never seen a real world example that also integrated wireless clients that had adjustable frames and used it to a generalized increase in file transfer performance.

And if you're in a setup where it is configured and giving you that small performance advantage, as soon as you start moving smaller (more everyday) file sizes & types across the LAN jumbo frames will be a performance detriment. The primary activity I use my LAN for is PC backup and I don't utilize a backup method that packages up files into large uninterrupted bundles.

And all packets you'll be txfring through from WAN to LAN, those packets will usually be at MTU 1500, so IIRC turning on jumbo frames will have either a neutral or negative impact on the Internet connectivity throughput. I could be mistaken on that one, I'd have to double check.

You cited a couple of PCs on your LAN w/ SSDs, in my experience that is probably the single biggest factor (after accounting for the use of gigabit Ethernet hardware and connections) in high file transfer speeds between PCs or my NAS.

You can use ping -f -l (packet size) [destination IP] from a command line to test out if larger frames are even being transmitted through from one device to another, but then your overall benefit is still dependent upon consistent MTU size between all devices on LAN/WLAN(?) and the actual network traffic you routinely send between machines.

Also as more stuff goes to IPV6, it has a "do not fragment" header in its packets by design. They use automatic MTU discovery to try to maximize packet efficiency. I have native IPV6 from my ISP, and my router and almost all my devices have it enabled, I'm not sure what - if anything can be modified to extract increased performance from its configuration.

 

[dolftb]

Thanks PrivateJoker for your info. I am not a network specialist and you have me thinking about just leaving all jumbo frames off.

Currently is only seem to get a boost in large file transfer speed from Nas on Router to PC behind Media Bridge when I only enable the jumbo frames on the router. I wonder why this is? don't mak eh no sense to me for the reasons you stated.

 

[PrivateJoker]

Thanks PrivateJoker for your info. I am not a network specialist and you have me thinking about just leaving all jumbo frames off.

Currently is only seem to get a boost in large file transfer speed from Nas on Router to PC behind Media Bridge when I only enable the jumbo frames on the router. I wonder why this is? don't mak eh no sense to me for the reasons you stated.

That's a good question, try that ping command from the PC to your NAS's IP with and without jumbo frames enabled at the router. I gotta think anything over 1500 will not have an unfragmented outcome if they're turned off in NAS & PC. You're in the grey area between the depths of "why doesn'ts" and a tacit acceptance of the "what is." I drift back and forth continuously myself.

 

[Igb]

A bit of necromancy to say the same works for me. (my setup is nas--main router(AC68U):::repeater router(AC66U)--switch--pc where -- means cable and ::: wireless link)

Quite odd. Actually with "jumbo trace" enabled in RT-AC68U got speeds about 10-20mb faster that without it. My MTU is still 1500 in all my devices so I am not using jumbo packets at all.

I was having about 15mb-ish transfers from pc to NAS. Actually i get 25-30mb/s (with peaks of about 38mb/s, the same aproximate value i get with iperf and 2+ streams).

My internet does not seem slower, and my ping remains roughly the same, so i think I'm keeping it this way.

Regards