Kim Barloso

Formatting the disk: What is the preferred cluster size


Question .

I bought a 1TB hard disk, it has 1 NTFS partition. I intend to keep all data on it. When formatting, I need to specify the cluster size. Sizes range from 512 bytes to 64 KB. Which option to use when formatting or can I leave the default cluster size unchanged?

What is the cluster size

The cluster size (allocation unit) is in other words the minimum size of blocks on a hard disk or other storage medium needed to store /files.

For the majority of HDD/SSD and user tasks you can leave the default setting provided by the OS, which is 4096 bytes. This cluster size is standard in Windows for almost all the disks up to 16TB.

General Tip

In short, the smaller /files will be kept on the disk, the smaller should be the cluster size. With this you can improve the performance of your hard disk or SSD a little bit, due to the fact that more blocks will be involved.

So if you have a lot of large /files (videos, music, etc.), you can define a larger cluster size. This way you will use less disk space.

The read/write performance of big /files will be better but the disk efficiency will be a bit lower.

  • For usb flash, sd cards with photos, music and documents a larger cluster size than standard can be used.
  • For the formatting of the Windows boot disk use the standard settings.
  • For standard purposes, for hard drives up to 3TB, if you have a lot of small /files, it is possible to reduce the cluster size, but this may result in reduced performance. We suggest setting the cluster size to 8KB for most situations. The preferable file system to use would be exfat
  • When using RAID and logical disks a 64KB cluster size would be a better choice.
  • For an SSD disk there is no reason to change the initial cluster size, typically 512 bytes. SSD performance is already fast enough without additional optimization. Additionally, SSDs need no defragmentation. Increasing it will only make things worse and generate more requests to the disk, which is not an optimal solution.
  • For large disks of 1-2TB or more, with multimedia data (movies, audio), you can define a cluster size a bit larger than the standard one. 4Kb will be just fine. However please be aware that suboptimal cluster distribution will result in a waste of disk space.

Pitfalls. Specialized software and system utilities (disk scanning, defragmentation) may have difficulties with non-standard cluster sizes - take this into account.

How to find out the cluster size on the disk

The instruction applies to any version of Windows including Windows 10.

  1. Open the console via Start > cmd (enter command into search)
  2. Run the console as Administrator. To do this use the context menu "Run as administrator".

  3. In the command line enter

fsutil fsinfo ntfsinfo C:

where C is the name of the disk to obtain data.

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Kim Barloso