NetBoot overload?

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NetBoot overload?

We're finding is when we NetBoot an entire lab of 31 iMacs at a time, Often times 6-9 of these iMacs will fail to pickup the NetBoot image and will (time out?) and revert back to the local disk for booting. Of the 20 or so iMacs that successfully NetBoot, only about half will have netbooted diskless. We need all 31 NetBooted in a diskless state.

Does anyone have any ideas why we might be having so much trouble getting 31 systems to NetBoot reliably? My thinking is it has something to do with the way our networking gear is configured, but our network guys have reviewed a ton of online material and seem certain the gear is configured correctly. Could the problem exist with how our servers are configured? Any help would be greatly appreciated.

Cheers,

Ev

Our gear..

• 31 2013 iMacs in each school across our district

• each school has a new Mac mini server running OS X 10.8 Server with Promise RAID attached

• our school networks are made up of Cisco gear (gigabit switches)

Posted on Aug 15, 2013 11:46 AM

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Answer 1

Aug 16, 2013 2:33 AM in response to designev

Netboot is mostly about fetching a huge file from the server. Because Netboot cannot depend on a full operating system with complicated network handling, the code to fetch this huge file isn't as clever at handling network problems as a computer with a proper operating system.

My guess is that if you try to boot all 31 of your iMacs at once, you are flooding the local piece of your network with traffic and some of the packets fail to get to their destinations. And the 'retry on failure' code isn't brilliant because it all has to be programmed into a computer without an operating system.

Try booting a maximum of 20 iMacs at once. Just for testing purposes. If that makes a big difference to your number of failures then you have something to investigate.

Also, if the NetBook image is on the RAID server, try moving it to the internal hard disk. Again, just for testing.

PS: Although those switches are gigabit switches, they can be programmed to run individual ports at slower speeds. You could ask your network people whether they have done this. This same is also true of the connection to your NetBoot server.

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