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Old April 1, 2014, 10:51 AM
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Default PLEASE HELP! Server Memory Question - split ranking on shared VM resources?

Hey gang, I'm hoping someone is familiar enough with server memory to answer this...

My company has 2x DELL R710's operating as shared resources for multiple VM's. (ESXi) At the moment, they each server has 6x 16GB of quad ranked DIMM's. We want to maximize our available resources on these servers, but if we stick with quad ranked RAM, then we're capped at 12 DIMM's per server of a possible 18. (192GB) However, we're considering moving all our existing RAM to a single R710, then filling up the other R710 with dual ranked RAM for a total of 288GB.

My question is; if the 2 servers are shared resources for a pool of VM's, is the above even possible? Will it mess up anything to have a combination of dual and quad ranked RAM as part of the shared pool?

Any help from a server guru would be appreciated. Thanks

*EDIT* - It's also important to note that we utilize vMotion across these two machines. So, does vMotion work across multiple ranks of memory?

Last edited by Caldezar; April 1, 2014 at 11:25 AM.
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Old April 1, 2014, 11:58 AM
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I am only guessing but to me logically it wouldn't matter because they are separate servers but I am curious if I am correct
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Old April 1, 2014, 04:27 PM
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In case anyone is interested; I finally got in touch with a Sys Admin over at VMWare and this was his response regarding the memory and an generational Xeon question:

Quote:
Based on what you described you shouldn't have any issues with the RAM. The VMs will not care want rank of physical RAM is being used on the hosts. As long as the vSphere hosts supports the hardware you're using you'll be fine.

Regarding vMotions between different generations of CPUs, the short answer is "Yes, it works." You need to use a vSphere cluster feature called Enhanced vMotion Compatibility (EVC). EVC instructs the hosts in your cluster to all present the same set of CPU features. Effectively it "hides" newer instruction sets that the older generation CPUs will not understand
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Old April 1, 2014, 04:28 PM
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The type of memory does not matter since the VM is independent of the hardware. VMotion should also be fine... though you will be limited to the memory of the machine you migrate to... so if you fill 80% of your 288GB machine and need to utilize vmotion you will have to make some decisions on what keeps running. If you are utilizing HA on all your VMs then thats a different story and you should look at the servers like a RAID.

In short type of memory does not matter, just your size difference might matter depending on your use case.
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Old April 1, 2014, 04:29 PM
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Quote:
Originally Posted by BlueByte View Post
The type of memory does not matter since the VM is independent of the hardware. VMotion should also be fine... though you will be limited to the memory of the machine you migrate to... so if you fill 80% of your 288GB machine and need to utilize vmotion you will have to make some decisions on what keeps running. If you are utilizing HA on all your VMs then thats a different story and you should look at the servers like a RAID.

In short type of memory does not matter, just your size difference might matter depending on your use case.
Thanks for the response Blue. You're right in line with the response from VMWare.
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