Blog6 VMware Server Migration Best Practices


While virtualization technology has been around for a while, it’s by no means a data center commodity as yet. But recent research from SpiceWorks suggests that adoption rates continue to rise across SMBs and enterprises alike.

With that in mind, it’s always smart to address best practices for successfully migrating physical servers to virtual servers. Here are six VMware best practices to make the most of your virtualization technology investment.

1. Create Operating System Templates

The Physical to Virtual (P2V) migration capability from VMware automates and simplifies physical to virtual machine conversions. Although P2V certainly eases the initial migration from physical servers, it can ultimately waste your virtual resources. With P2V, physical servers’ devices (e.g. serial bus) and associated drivers are replicated to the virtual server even though many of them may be unnecessary or unavailable. Additionally, P2V creates virtual server images with the same physical attributes as the physical servers, often resulting in an over-allocation of resources. Instead, use the VMware capability to create image templates of different operating systems. Later, you can use these templates to deploy a new virtual server in a matter of minutes.

2. Create Single Processor Images

As you create operating system templates, make sure they’re single processor images. Guest operating system images share physical processors, so in most cases, virtualized single processor guest operating systems perform much better than multi-processor guest operating systems. For example, a multi-processor guest operating system will be scheduled for time slices on multiple physical processors, increasing scheduling time and resources utilized—which adversely affects the resource pool available to the other guest operating systems.

3. Minimize the Resources Allocated to Virtual Servers

Typically, virtual instances of a server require less processor and memory resources than their physical counterparts. That’s because physical servers are often over-configured with memory and processing power—and you can’t dynamically expand physical resources, as you can with virtual servers.

To achieve the maximum performance levels, minimize the resources allocated to virtual servers. Deliberately set the processor and memory resources low. Then closely monitor the guest operating system resource utilization over an initial evaluation period. Increase the processor and memory resources only when necessary, preventing allocation of unneeded memory and processor capacity to a virtual server. This also prevents unneeded consumption of resources that you could make available to other virtual servers.

4. Beware of SCSI Reservations

SCSI reservations are used for specific operations when metadata changes are made, and they prevent multiple hosts from concurrently writing to the metadata. You might see this situation when you:

  • Create or delete a VMFS datastore
  • Expand a VMFS datastore onto additional extents
  • Power on or off a Virtual Machine (VM)
  • Create a new VM
  • Migrate a VM with vMotion
  • Grow a snapshot file or a thin-provisioned Virtual Disk

While SCSI Reservations are necessary to avoid data corruption, they also degrade the performance of virtual servers. To help minimize SCSI reservations, you can:

  • Only use vMotion to migrate a single guest operating system per LUN at any one time
  • Only cold migrate a single guest operating system per LUN at any one time
  • Avoid powering on/off too many VMs simultaneously
  • Limit template creations and deployments to a single creation per LUN at any one time
  • Limit the number of running snapshots—snapshots grow in 16MB increments, and each time they grow, they cause SCSI reservations

5. Keep Operating System and Application Data Sets on the Same Volume

In physical servers, the operating systems and the application disks are separate. However, in a virtual server environment, you should keep both the operating system and application on the same volume. When all of the disk space in the virtual server environment is in the storage array, you get RAID protection and multiple physical disks. A single volume also eliminates the need for consistency groups across multiple volumes, ensuring that the operating system and application snapshots are performed at the same instant. Furthermore, keeping both the operating system and application on the same volume simplifies the snapshot and recovery process.

6. Keep at Least One Physical Active Directory Server

Be sure to keep at least one physical active directory server. If your data center experiences an event that disrupts the entire ESX infrastructure, you can bring this server up before the virtual servers. That way, you’ll avoid the manual process of managing the order in which you start the virtual servers, and you’ll ensure your virtual servers are able to complete their boot processes.

Virtualization technology can dramatically improve the efficiency and availability of resources and applications in your organization, helping you maintain your company’s competitive edge—this makes your decision to implement a virtualized infrastructure both cost-effective and strategic. Ideally, your virtualization technology implementation should maximize your existing resources and provide an infrastructure that is scalable, available, and reliable for all your company’s applications. Use these best practices to ensure successful VMware deployments that will optimize performance and utilization.

About the Author

Dustin Smith

Dustin Smith, Chief Technologist

Throughout his twenty-five year career, Dustin Smith has specialized in designing enterprise architectural solutions. As the Chief Technologist at ASG, Dustin uses his advanced understanding of cloud compute models to help customers develop and align their cloud strategies with their business objectives. His master-level engineering knowledge spans storage, systems, and networking.