Windows 10 and Freenas cifs performance different MTU

[Morpheus187]

Hi there

I'm experimenting with different MTU settings and CIFS-Performance.

When MTU is set to 1500 ( default ) I have the following perfomance:
Windows10 to Freenas -> ~100 MB/S
Freenas to Windows10 -> ~105 MB/S

When MTU is set to 9000 I have the following performance
Windows10 to Freenas -> ~ 75 MB/S
Freenas to Windows10 -> ~118 MB/S

What I don't understand is, why I've got slower performance while transferring from Windows 10 to Freenas with an MTU of 9000 when the transfer in the other direction is faster?

I tried out different network adapter settings on the Windows10 side without effect. ( Large Send Offload V2 to Disabled )
I also fired up wireshark and looked at the pakets and could see a small anomaly, the ack packets differ in the "Win" attribute.
Windows10 to Freenas -> Win=980 (800-1000)
Freenas to Windows10 -> Win=64960

It looks to me that Freenas is telling Windows10 to send a bit slower, but it continues to send 9014 byte packages and is told again to be slower, so this results in a overall slower transfer rate.

I then did some test with iperf and they show the same result, speed from windows10 to freenas with MTU 9000 is slower than with MTU 1500
614 MBits (MTU 9000 ) versus 939 Mbits ( MTU 9000 )

I thankfull for any hint, maybe there is a sysctl which I can try to improve network performance? I don't know if they are applied instantly or if I need to reboot freenas.

Thanks

Morpheus

 

[joeschmuck]

I think you need to do a little research on MTU optimization and does your hardware support jumbo frames. Additionally you didn't specify how you were running the testing nor the hardware configuration of both systems and the interface paths. I can't say if FreeNAS 10 Beta has any problems but I can ask you if you have tried this test using FreeNAS 9.10.1? Does that work better, worse, or the same? Another thing to try is a direct Ethernet connection between the two systems.

BTW, your default performance is very good, you won't squeeze much more out of it, but then again I don't know how you are testing so it's tuff to figure out how valid the results are.

 

[Morpheus187]

Hi

Thanks for the reply

I've worked around with different settings and then speed went down to 70 MB/S. Then I rebootet everything and it worked, both directions 118 MB/S. ( wireshark showed a tcp window size increase )
But when I upload and download large files at the same time, the performance drops to 2 MB/S :(

So I decided to give up my "Jumbo Frame" experiment and go back to standard 1500 MTU. Which is now working fine again. ~100-110 MB/S transfer in both directions. ( ~ 70 MB/S when up and Downloading at the same time -> 140 MB/S combined )

for further reference:
The Freenas box is a 9.10 Stable release machine with 32 GB ECC-Ram, 8x6 TB Storage, RaidZ1
Network is going over 2 switches and about 40 meters of cat 6 cable
All the hardware is jumbo frame capapable
Test was done with a large movie file ( 5 GB ) and samba/cifs protocol.


Thanks

Morpheus