Why should we reduce or decreasing the RAM at all? It is often the case that only limited resources are available in a LAB/Homelab. In these cases it is necessary to reduce the CVM Memory from 16GB to 8GB. In this short article I will show you how this can be done after installation.

Attention: If you give 8GB of memory you will get in PRISM warnings that the memory of the controller virtual machine is running low. Either disable the alarm, or give the CVM more RAM again.

It may also be that the cluster has less performance, but this should be sufficient for a test scenario. If you want to test your performance, leave the controller virtual machine memory at 12GB or more.

Decreasing CVM Memory from 16GB to 8GB

First we go to the host via SSH where we want to shrink the CVM (Nutanix Controller Virtual Machine) memory (root/nutanix/4u).

#ssh root@10.42.10.20

With virsh list –all we display all VMs on the Nutanix CE node. Important for us is the VM endent with CVM.

[root@NTNX-f792168d-A ~]# virsh list --all
 Id    Name                           Status
----------------------------------------------------
 2     NTNX-f792168d-A-CVM            running

To change the memory, we have to shut down the CVM with virsh shutdown CVM Name.

[root@NTNX-f792168d-A ~]# virsh shutdown NTNX-f792168d-A-CVM
Domain NTNX-f792168d-A-CVM is being shutdown

[root@NTNX-f792168d-A ~]# virsh list --all
 Id    Name                           Status
----------------------------------------------------
 -     NTNX-f792168d-A-CVM            shut off

Now we can reduce the memory from 16GB to 8GB using virsh setmem and virsh setmaxmem.

[root@NTNX-f792168d-A ~]# virsh setmem NTNX-f792168d-A-CVM 8G --config

[root@NTNX-f792168d-A ~]# virsh setmaxmem NTNX-f792168d-A-CVM 8G --config

Then we start the CVM (virsh start CVMName) and check if the settings have been applied. To check that the settings have been applied correctly, we use the command “virsh dominfo CVMName”.

[root@NTNX-f792168d-A ~]# virsh start NTNX-f792168d-A-CVM
Domain NTNX-f792168d-A-CVM started

[root@NTNX-f792168d-A ~]# virsh dominfo NTNX-f792168d-A-CVM
Id:             3
Name:           NTNX-f792168d-A-CVM
UUID:           6793299e-77b0-42b4-a422-81ed75d33afd
OS Type:         hvm
Status:         running
CPU(s):         2
CPU time:       5,7s
Max memory:   8388608 KiB
Used memory: 8388608 KiB
Persistent:     yes
Autostart:      enable
Managed save:   no
Security model: selinux
Security DOI:   0
Security label: system_u:system_r:svirt_t:s0:c14,c102 (permissive)

Now the controller virtual machine should run with 8GB memory instead of 16GB. Repeat these steps with all CVMs in your cluster.

Only one CVM should be switched off at a time. If all are to be changed at the same time, stop the Nutanix CE cluster first. Therefore you can execute the command “stop cluster” on any CVM via SSH.