Virtual Machine Advanced Configuration Options

First and foremost, it is worth mentioning, that it is definitely not recommended to change any advanced settings unless you know what you are doing and you are fully aware of all potential impacts. VMware default settings are the best for general use covering the majority of use cases, however, when you have some specific requirements you might need to do the VM tuning and change some advanced virtual machine configuration options. In this blog post, I'm trying to document advanced configuration options I've found useful in some specific design decisions.

Time synchronization

• time.synchronize.tools.startup
• Description:
• Type: Boolean
• Values:
• true / 1 (default)
• false / 0
• time.synchronize.restore
• Description:
• Type: Boolean
• Values:
• true / 1 (default)
• false / 0
• time.synchronize.shrink
• Description:
• Type: Boolean
• Values:
• true / 1 (default)
• false / 0
• time.synchronize.continue
• Description:
• Type: Boolean
• Values:
• true / 1 (default)
• false / 0
• time.synchronize.resume.disk
• Description:
• Type: Boolean
• Values:
• true / 1 (default)
• false / 0

Relevant resources:

• VMware KB - Disabling Time Synchronization (1189)
• Completely Disable Time Synchronization for your VM

Ethernet

• ethernetX.rxDataRingEnabled
• Description: When set to true, Receive Data Ring is enabled 
• Type: Boolean
• Values: true/false, 1/0
• Relevant resources:
• VMXNET3 RX Ring Buffer Exhaustion and Packet Loss 
• ethernetX.pnicFeatures
• Description: Enable specific pNIC features for particular VM vNIC
• Type: Int
• Values:
• 4 - Enable multi-queue (NetQueue RSS) in particular VM vNIC
• ethernetX.ctxPerDev
• Description: Enable transmit traffic multi-threading for VM or vNIC
• Type: Int
• Values:
• 1 - one CPU thread per vNIC
• 2 (default) - one transmit CPU thread per VM
• 3 - multiple (2 to 8) TX threads for particular VM vNIC
• Relevant resources:
• How to optimize Virtual machine vNIC transmit (Tx) performance?
• Best Practices for Performance Tuning of Telco and NFV Workloads in vSphere
• ethernetX.udpRSS
• Description: vSphere ESXi 6.7 supports Receive Side Scaling (RSS) for UDP which provides a significant improvement in throughput. Use this feature for workloads that are sensitive to network latency and bandwidth. 
• Type: Boolean
• Values:
• true / 1
• false / 0 (default)
• Relevant resources:
• Enhance NSX Edge Performance after ESXi Host Upgrade

Isolation

With the isolation option, you can restrict file operations between the virtual machine and the host system, and between the virtual machine and other virtual machines.

VMware virtual machines can work both in a vSphere environment and on hosted virtualization platforms such as VMware Workstation and VMware Fusion. Certain virtual machine parameters do not need to be enabled when you run a virtual machine in a vSphere environment. Disable these parameters to reduce the potential for vulnerabilities.

Following advanced settings are booleans (true/false) with default value false. You can disable it by changing the value to true.

• isolation.tools.unity.push.update.disable
• isolation.tools.ghi.launchmenu.change
• isolation.tools.memSchedFakeSampleStats.disable
• isolation.tools.getCreds.disable
• isolation.tools.ghi.autologon.disable
• isolation.bios.bbs.disable
• isolation.tools.hgfsServerSet.disable
• isolation.tools.vmxDnDVersionGet.disable
• isolation.tools.diskShrink.disable
• isolation.tools.memSchedFakeSampleStats.disable
• isolation.tools.guestDnDVersionSet.disable
• isolation.tools.unityActive.disable
• isolation.tools.diskWiper.disable

Relevant resources:

• Configure Advanced Settings on All Management Virtual Machines for Compliance with NIST 800-53 
• Disable Unexposed Features

Snapshots

• snapshot.maxSnapshots
• Description: Limit the number of snapshots of Virtual Machine
• Type: Int
• Value: max number of snapshots
• Relevant resources:
• "A general system error occurred: Exceeded the maximum number of permitted snapshots" error when creating a virtual machine snapshot (1031280)
• How to control maximum number of VMware snapshots

Remote Display

• RemoteDisplay.maxConnections
• Description: Limit the number of simultaneous connections to Virtual Machine
• Type: Int
• Value: max number of snapshots
• Relevant resources:
• Opening a console to a virtual machine fails with the error: Unable to connect to the MKS: Console access to the virtual machine cannot be granted since the connection limit of 0 has been reached (2015407)