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Shares settings in ESXi

Posted on 2011-05-12
Medium Priority
Last Modified: 2012-05-11
Can anyone explain the "Shares" setting in the Resource Allocation section of ESXi. I am working on a project that sends a constant stream of high bit rate UDP traffic through a CentOS Linux VM. I have noticed that ANY activity using vSphere Client or other VM's causes packet loss on the UDP stream.

Since processing UDP traffic seems to be processor intensive, I am trying to figure out if I can isolate that VM for CPU, Memory, and Network resources. The VM for this application has 2 dedicated Ethernet NICs that aren't shared with any other vSwitch.

The server I am using has a quad core 2.5G processor, 8G RAM and 8 physical Ethernet ports. I have reserved 2.5Ghz of processing for this Linux VM, and wondered if the shares setting will eliminate the errors when other things are going on with other VM's or the host itself.
Question by:kcchalk
LVL 124
ID: 35748575
My advice, is not change them.

How sensitive is the processing of UDP Traffic?
LVL 124
ID: 35748601
Secondly is this a realtime application?

I then maybe I'll try to explain?

Author Comment

ID: 35748664
It is a real-time application. The data originates from a TDM (Time Division Multiplexing) source,  so packet loss and jitter are critical components to ensure data integrity. The rate can vary from 50-60 packets per second all the way up to 1000 packets per second.
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LVL 124

Accepted Solution

Andrew Hancock (VMware vExpert / EE MVE^2) earned 2000 total points
ID: 35748755
Okay, it shoulds very similar to issues we've been experiencing with VMware Virtual Machines when using VOIP servers and applications, which shares a similar theme, real time, TCP and UDP traffic.

The issues we've been working on with vendors and VMware (for a while)  is the CPU algorythm scheduling function, causes issues with the UDP traffic.

At this time VMware have recommended not to deploy any VOIP applications on VMware vSphere. (yet!).

So the issue you are experiencing seems very similar.
LVL 124

Assisted Solution

by:Andrew Hancock (VMware vExpert / EE MVE^2)
Andrew Hancock (VMware vExpert / EE MVE^2) earned 2000 total points
ID: 35748881
also have a look at this white paper

VMware vSphere The CPU Scheduler in VMware ESX 4.1


vSphere Resource Management Guide

LVL 30

Expert Comment

ID: 35749826
are the 2 vnics in a port group

Author Comment

ID: 35749898
Separate port groups. I have only 1 physical NIC per port group, per VM running UDP traffic.

So, For example, Linux VM-1 has eth0 and eth1, and eth0 is a port group with a single NIC and eth1 is a port group with a single NIC. I did this to prevent any contention (or so I thought) for resources at the NIC layer.

Seems to me with all the settings and customization you can do, there ought to be a way to isolate the resources for a single VM, especially in a multi-core, multi-ethernet, adequate memory system.

Author Comment

ID: 35749904
I am going to read the white papers you referenced, thank you for that.

Author Comment

ID: 35755081
One specific question. I ran the UDP application inside the Linux guest, and performed a snapshot of that VM using vSphere client, and my application started taking hits during the snapshot, and had a hard time recovering.  Is there any way to isolate a VM from management functions of vSphere?
LVL 124
ID: 35755122
Snapshots will have that affect on any running VM, because it freezes the Virtual Machine for a very short time.

It's ESX Server that has the issue, we tried altering the scheduling frequency of the processor scheduling feature, the default is 20ms, before it moves the process to the next core. It didn't work.

We are waiting and testing newer features, it is hoped that there will be some changes in the next release of vSphere 5.0, to support VOIP. Until then, VMware recommends you should not try and use vSphere Virtual Machines for VOIP or similar based applications.
LVL 71

Expert Comment

ID: 35944408
This question has been classified as abandoned and is closed as part of the Cleanup Program. See the recommendation for more details.

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