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Specifying the Most Appropriate Cluster Size While Formatting

When file is stored in storage media it occupies some pre-defined slots, known as sectors. These sectors are grouped to form cluster. The cluster size depends on the file system which is: NTFS, FAT or FAT 32. These cluster size varies from 4096 bytes to 64 kilobytes according to the selected file system.

A cluster is allowed to be accessed by only a single file; which means a single cluster cannot be shared by two files. In such case, if a file occupies a fraction of cluster then the remaining sectors cannot be used by any other file. This case is repeated for all the clusters. So, bigger the cluster size more is the wastage of storage. Small cluster size enables you to efficiently store files and utilize maximum sectors available.

The cluster size also defines the speed of accessing the files. For large cluster size, files will be less segregated; while for small size a single file is divided in to different clusters. To read a file all the clusters associated with it are assembled. So, bigger the cluster size is; the faster the file is fetched.

So it is very important to decide the appropriate cluster size. You must decide the cluster size keeping your priority in mind. If the requirement is system performance, you may choose large cluster size; but if effective memory-allocation is needed, you must select small cluster size. The cluster size can be decided during formatting drives or any other storage media.

Steps for defining cluster size:-

  1. Log on to the Windows using administrator account.
  2. Open Computer by going to Start menu and clicking Computer.
  3. Right-click the drive or the storage media that is to be formatted.
  4. Select the Format option.

  5. In the dialog box, under Allocation unit size, click the drop-down list and select the desired cluster size. (Default cluster size is 4096 bytes.)

  6. After selecting the correct cluster size, click Start to start the formatting process.
  7. On the displayed warning box, click OK to continue.

  8. Wait till the drive gets formatted.
  9. Click OK when done.

  10. Close the format dialog box.


  • Note: Make sure that before formatting any drive or storage media, there is no data stored or you have a backup of the stored data, otherwise you will lose all of it. So before formatting, it is always recommended to create a backup of the stored data.
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