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network disconnects on 2012 Mac minis

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Alex Gerulaitisnetwork disconnects on 2012 Mac minis
by on Feb 10, 2015 at 10:38:38 am

We have several 2012 Mac minis in our server room that reliably disconnect from 1GbE network (but otherwise appear to still be working) when the adjacent servers are under heavy CPU load.

We suspect RFI / EMI but can't be 100% sure as we don't yet have a good way to measure it and isolate the source. Other servers (over 50, all kinds including a bunch of xserves) in the same room are fine. Taken out of the server room, Mac Minis are fine.

The weird parts:
- the disconnects started happening after we added three new servers (render nodes) to an existing cluster of three, pretty much pinpointing them as the source of the issue
- no issues when those servers are idle
- issue seems to start when all six are under 50% or higher CPU load
- all other devices in the server room - lots of them, all kinds - have no issues; only the Mac minis are affected

What would you recommend to troubleshoot and address the issue? (Outside of powering down those new render nodes - which we do need and which don't seem to affect anything else.)

P.S. What we haven't done yet:
- to check for a possibility that it's just one server misbehaving, disconnect servers one at a time while putting remaining ones under 100% CPU load
- research RFI / EMI measurement and isolation equipment and services
- attempt to ground the Mac minis (their power cables are 2-prong, aren't grounded) or otherwise shield them from RFI / EMI

We do need the Mac minis as we're running out of Xserves, and certain apps we need only run on Macs.

P.P.S. Wasn't sure where to post this: there's a Windows hardware" forum but not "Apple hardware" or generic hardware forum, it seems.

Thanks for any ideas!

-- Alex Gerulaitis, sysadmin, DATG

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Tyler ChittickRe: network disconnects on 2012 Mac minis
by on Feb 25, 2015 at 1:42:24 am

Could the Minis be overheating? I would try checking that as well in your list of checks. Otherwise, you might take that issue to Apple themselves.

Tyler Chittick
Integration & Technical Support
Maxx Digital

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Alex GerulaitisRe: network disconnects on 2012 Mac minis
by on Feb 26, 2015 at 7:59:25 am

Wish it was that simple... They're sitting idle in the server room at 65 degrees. If anything, they're freezing! :)

Tracked it to spikes in network traffic - and only 2012 Mac Minis are affected - regardless of the physical location - as long as they're wired to the network.

Will try WiFi. Also looking to borrow someone's 2014 Mac Mini for a couple of days to test - so far no luck. Suspect it'll behave better.

Thanks for trying to help.

(Getting enterprise support from Apple? You serious? :))

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Alex GerulaitisRe: network disconnects on 2012 Mac minis
by on Mar 7, 2015 at 3:32:55 am

FWIW, the problems disappeared after one of the servers was off-lined. The server was HP 360 G8 with a quad-port 331FLR NIC. I've seen other people having issues with that NIC, however our problem was really bizarre, a perfect storm of seemingly unrelated circumstances that would not be easy to reproduce.

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