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Get the allocation unit size with PowerShell

The allocation unit size or named block size of a partition is important for the systems. Think about the system performance. A partition is default formatted with a standard 4KB allocation unit size. This does not mean that it’s the best practice. In fact, Microsoft recommends that partitions have 64KB allocation unit size for SQL Servers and Exchange Servers. In this article, you will learn how to find the partitions allocation unit size with PowerShell.

Information about the allocation unit size

Before we start to find the partition allocation unit size or named block size. It’s good to know the difference between disk, volume, and partition. A disk does have one volume, the volume can be split into multiple partitions.

For example, you have a 100GB disk. This means that the volume is 100GB. You can split the 100GB volume into partitions of the size 20GB, 20GB and 60GB. You will have one or more partitions. In every partition, a different allocation unit size can be set.

The allocation unit size can be set differently in every partition.

Get the allocation unit size with PowerShell

We like to get the allocation unit size on all the partitions of the Exchange Server EX01. We are going to use the Get-cimInstance cmdlet. Run PowerShell as administrator.

BlockSize 65536 = 64KB allocation unit size. BlockSize 4096 = 4KB allocation unit size.

As a result, we have 10 partitions on the EX01 server, an explanation of every partition:

  • System partition is hidden. The partition is created by default when you install an Operating System (OS).
  • DB01/DB02/DB03/DB04 Data and Logs partitions are the Exchange database data and logs.
  • OSDisk partition is the Operating System (OS).


To summarize, you learned how to get the allocation unit size with PowerShell. If you have SQL or Exchange Servers, make sure that the block size is 64KB. Microsoft did write a great document about the Get-cimInstance cmdlet. Did you enjoy this article? If so, you may like the article Add UPN suffix in Active Directory. Don’t forget to follow us and share this article.



ALI TAJRAN is a passionate IT Architect, IT Consultant, and Microsoft Certified Trainer. He started Information Technology at a very young age, and his goal is to teach and inspire others. Connect with ALI TAJRAN on social media. Read more »

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