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Mac 10GbE network - 9000MTU required?

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Chuck Kenney
Mac 10GbE network - 9000MTU required?
on Jul 15, 2016 at 6:54:29 am

I inherited a new client who has a few newer Mac Pros (Mac OS 10.9.5) with Promise SanLink2 10Gbit adapters, a handful of MacBook Pros with gigabit and wifi, and a Mac Mini server (10.10.5) with a SanLink2 10Gbit adapter. They've been complaining about speed to the server from the video workstations. Everything is on the same subnet. Connections are via AFP.

Was getting about 250-300MB/sec transfer rates between any of the 10Gbit machines. The server and the workstations had both AirPort on and the SanLink2 adapters connected. The server had it's MTU set to 9000, the workstations set to 1500. (this was all before I touched it)

I updated the SanLink drivers, then to simplify things (and hindsight, may have been a mistake), I turned off AirPort on the Mac Mini server, and the Mac Pros.
As a test, I changed the MTU on the Mac Pros to 9000, and set the adapters with the sanlink utility to high performance. Transfer rates between the Mac Pro's went up to 800-900MB/sec, and between the Mac Pros and the Mac Mini to around 600MB/sec.

Now, connecting to the server from the wifi and 1Gbit machines is insanely slow (15+ minutes per folder listing), and I assume this is due to the MTU difference between the different parts of the network. As a temporary fix, I turned wifi back on, on the Mac Mini server, and speeds from the wifi and 1Gbit machines is back to about 15 seconds per folder listing (still slow, but apparently that is how it was months ago).

I have made no sysctl changes.

So... here's my question for any gurus who have set up network video storage. Is 9000 MTU required for solid performance on the Macs over 10 Gigabit, or just sysctl changes. Basically, am I looking at setting up two subnets so I can separate the networks properly and not have packet size issues? (That, and I'm confused that they weren't having more issues if that is the case, since the server has been at 9000 MTU for who knows how long).
Or, set every single Mac and device in the building to 9000 MTU, even the wireless ones.

Here's a network diagram of the current setup. Unfortunately I don't have the exact models of some of the equipment with me at home to note on this chart.

http://creately.com/diagram/example/iqn8u4tr2

If this is the wrong place to ask a question like this, I will gladly nuke the post too, and apologize.


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Bob Zelin
Re: Mac 10GbE network - 9000MTU required?
on Jul 15, 2016 at 4:37:52 pm

simple answer -
two networks - two switches. Everything works.

And the Mac Mini is a terrible server for four clients all running 10G speeds. You are sharing one Tbolt buss with your drive array

Bob Zelin

Bob Zelin
Rescue 1, Inc.
bobzelin@icloud.com


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Chuck Kenney
Re: Mac 10GbE network - 9000MTU required?
on Jul 17, 2016 at 7:26:21 am

Thanks Bob. Re-configuring and making it two networks next week. And they're aware that they may need to budget to replace the server as well.


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