Terrible performance VM since HW upgrade 4->7

[Frans_P]

Hi everyone,

We have some VM's running on which the hardware has been upgraded from version 4 to version 7. Everything was working properly after the upgrade.

Now, we have found out that when adding more resources on the VM, the VM gets terrible slow. For example, when i run taskmgr.exe it takes about 5 seconds to start and it takes 33% CPU load on a VM with 4GB RAM and 4 sockets. When we reconfigure the resources to the settings they where, everything is fast again.

Anyone?

Best Regards,

Joris Kemperman

[schepp]

Hi,

more vCPU doesn't mean more power / faster VM. Often a VM with only one vCPU is faster.

Simple example:

a Host with 2 Quadcores = 8 cores.

4 VMs with 4 vCPU = 16 "cores"

Means every physical core has to do the work for 2 vCPUs.

@ all: don't hit me because I didn't mention things like load balancing via vmkernel

[RParker]

When we reconfigure the resources to the settings they where, everything is fast again.

Along with what Shepp said, which was very well stated, did you test the VM BEFORE you added those resources? You probably don't need them.

The biggest problem new people get into with VM's is they want them to be EXACTLY like physical. WRONG!

VM's are not replacement for physical, they are for consolidation and management, not performance. VM's will run as fast as they can with usually 1 vCPU. Adding more is a waste.

[Frans_P]

Thanks for the answers, but: it shouldn't be normal that the VM gets terrible slow after adding 1GB of RAM, don't you agree?

When adding 1GB RAM for example, taskmanager suddenly takes 33% CPU load and needs 10 seconds to start....

The Host is using 60% of its resources.

[kashifsajjad]

I think there is nothing with hardware upgrade, there is some issues with the resources allocated to the VM

1) giving 4vCPUs is not meant that VM will run fast. it depends on your Physical Host. if for example your physical ESX host contains 01 Quadcore Scoket and you are running more than 01 VM on it and each VM has been assigned 4vCPUs, its not recomended as each vm can use 1 core of physical CPU for 20ms and then its switch back to other VM for 20ms. so if 02 VMs has been assigned 4vCPUs then they must have to wait for 20ms for each core to be available, which may cause the delay or performance issues so its better to assign Minimum CPU to VM's.

2) You can also used CPU Affinity Option to dedicate Physical Core Directly to VM (But is not recommnede as Other VM's cant able to use it)

3) Disable Hyperthreading Option for ESX Host on which the particular VM is running

4) Also check if ESX Host is suffering from Memeory Overhead that may cause VM to Slow

Hope these recomendations will help you