Virtual machine partition alignment (Partition alignment) questions and Answers

Q: What is partition alignment (partition alignment)?

A: This refers primarily to the partition needs of the client OS and the block alignment of the storage device. Specifically, the partition start Shift (PSO, Partition starting offset) should be a multiple of 4096. After a new installation of Windows 2008, Vista, and Win7, Partition starting offset is 1048576 and is already a multiple of 4096, so no adjustment is required. However, Windows xp,2000 and 2003 partition starting offset are 32256, not multiples of 4096. (Note that if the Win2008/7/vista is upgraded from a xp/2000/2003 version, the PSO will not change and there will be problems)

Q: Why do you want to partition alignment?

A: Failed to do partition alignment will bring down VM disk performance, waste processing power, and bring costs up. This negative performance may not be noticeable when the host platform is low on load, but the loss of disk performance can be magnified as the host load increases. So from the start of deploying a new VM, you have to be aware of this problem.

Q: How to judge if there is a problem of partition misalignment existing virtual machines?

A: You can know by system information. Run the msinfo32 command or enter Start→all Programs→accessories→system tools→system information from the Start menu.

Or it can be scanned using the Mbrscan tool provided by NetApp, as described below.

Q: For a new VM, how to ensure that the deployment will not cause partition misalignment problems?

A: If you are using a template to deploy a new VM, you should fix the problem when you install the VM template machine. This way the VM deployed through a good template does not produce partition misalignment problems

Q: When creating a new VM, how to align partitions?

You can start the virtual machine with the WinPE CD and use the DiskPart tool to create the partition and set the partition start offset directly. As shown in the following illustration:

Then install the operating system on this pre-built partition.

Q: If my VM already exists and the partition start offset is not a multiple of 4096, how do I correct it?

A:netapp provides a tool mbrtools that includes 2 executables, one mbrscan, to scan VMDK to see if it meets the requirements for partition alignment. The second is mbralign to solve the problem.