Slow WDS PXE Clients and Bad Memory
Following on from my post last week about UK Regional Settings for MDT 2013, I have been this week testing the deployment of a Lite Touch MDT image using WDS PXE over Multicast. Unlike what you will read online about Multicast, I haven’t personally had any issues with it and Multicast has worked off the bat but the problems I have been encountering are actually with Unicast, with the initial phase of PXE boot, downloading the Boot SDI and the WinPE LiteTouch WIM files.
In this case, I’ve been given eight client machines to test the deployment and we were finding that only about half of them were properly initiating the WinPE environment in a sensible timeframe with the other clients taking over 30mins just to download the Lite Touch WinPE image which obviously isn’t cricket as you should be able to lay down the entire Windows OS image is not much more time than that.
All of the machines are HP 8000 desktops with a matching hardware specification and matching firmware revisions so we were left wondering if the problem was the network, routing or such like however earlier on this afternoon, we found the issue and I have to say, it’s one of the craziest reasons I’ve seen something not working in a long time, especially considering how software defined our worlds have become.
Yes, that is correct, the above is an image of a Hynix 2GB PC3-1006U-9-10 DIMM and this was the cause of our problems.
The machines in question were all configured with 6144MB of RAM in the form of three 2GB DIMMs. What we didn’t notice at an early stage and why would you really, was that some of the machines exclusively had three DIMMs of HP certified Micron memory in them and our faulting machines had a combination of HP certified Micron memory and Hynix HP certified memory.
All the DIMMs were of the same unregistered type, all of the same PC3-10600 speed and all have the same 9-10 CAS latency so it’s just crazy to think that a mismatched batch of Micron and Hynix memory could ruin things for us given that all of the other factors like registration, speed, latency and ranking were matched.
Simply by removing the Hynix DIMMs from the machines and leaving them with 4096MB made up of two 2GB DIMMs of Micron memory allowed these machines to load the Boot SDI and Lite Touch WinPE WIM files at the speed we expected to see and were already seeing on the other clients.
When we look at this logically, you can see why our issue was a memory problem because the download of the Lite Touch WinPE WIM is done into memory and the hard disk is not touched at this point but I cannot remember the last time I saw a simple DIMM cause so much of a problem. These days we automatically assume that hardware works and that our problems exist in software due to the configurable nature of everything but this was certainly a lesson to never forget the simple things in computing: the basic hardware like processors, memory, motherboards and the like.