Set The Right Allocation Unit Size When Formatting a Drive

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Have you ever formatted a disk on your own?


Attempting to format a disk for the very first time?

Then, you should read this post, as it will tell you why setting the right allocation unit size is essential while formatting a drive.

Now, what do you mean by ‘Allocation unit size’?

It is also known as or can be addressed as ‘Cluster size.’ The cluster size can be defined as the tiniest chunk of disk space that holds a file.

When you begin to format a partition into one of the file systems such as NTFS, FAT, exFAT, etc., Windows makes use of the default values if formatting is done by one of the following methods:

  • By using the ‘FORMAT’ command from the command line without mentioning the cluster size;
  • When the Allocation Unit box in the Format dialog box lists Default Allocation Size while formatting a drive from Windows Explorer.

However, it is advisable to keep the allocation size small if many small files are present. This will help in saving disk space. But, if the size of the files is large, it is a good idea to keep the allocation size big. This will eventually enhance the system’s performance.

Our Hard drives are divided into clusters, and the allocation unit's size determines the size of a single cluster. The file system in which the hard drive is formatted keeps track of or records the clusters' state. When a file or a portion of the file is written on any cluster, it is marked as or considered to be occupied. If the size of the clusters is small, the speed with which the hard drive performs becomes slower. It happens because each file is broken into small pieces, and it takes a significant amount of time to gather all the broken pieces in one place and access them as one.

And, if the cluster size is large, the space on the disk will be wasted.

Hence, there is no absolute benchmark for setting the size of the allocation unit. If the size of the files you wish to store on the drive is large, then a large cluster size is recommended. This will also increase the speed with which the drive will perform. If you plan to store smaller-sized files, a small cluster size will do the deed. It will preserve the space on the disk.

Note: Formatting a drive into any file system comes with a catch. If the formatting is done improperly or the process is interrupted, you may lose the data on your drive.

Read: Here’s how you can retrieve an exFAT partition.

About the Author: John Harris

With a decade of experience in data recovery, John Harris, Senior Editor at Remo Software, is your go-to specialist. His focus includes partition management, Windows solutions, and data troubleshooting, delivering insightful content that serves both users and search engines. John's expertise shines through in illuminating blog posts, untangling data loss intricacies across diverse storage platforms.…