How to Check Disk Drive Allocation Unit Size on Windows
A terminal command to show the allocation unit size (bytes per cluster) for a specific drive
I was working on a task to ensure that the NTFS drives installed on several Windows PCs all use the same allocation unit size. I needed a reliable way to check this information.
As it turns out, it’s quite simple.
First, open the Terminal app as an administrator.
Then, run the following command:
fsutil fsinfo ntfsinfo {Drive_Letter:}Replace {Drive_Letter:} with the letter of the drive you want to inspect.
For example, to check the C: drive:
$ fsutil fsinfo ntfsinfo C:
NTFS Volume Serial Number : 0xe0123456789abcde
NTFS Version : 3.1
LFS Version : 2.0
Total Sectors : 998,553,599 (476.1 GB)
Total Clusters : 124,819,199 (476.1 GB)
Free Clusters : 65,667,461 (250.5 GB)
Total Reserved Clusters : 5,152 ( 20.1 MB)
Reserved For Storage Reserve : 0 ( 0.0 KB)
Bytes Per Sector : 512
Bytes Per Physical Sector : 4096
Bytes Per Cluster : 4096 (4 KB)
Bytes Per FileRecord Segment : 1024
Clusters Per FileRecord Segment : 0
Mft Valid Data Length : 3.83 GB
Mft Start Lcn : 0x00000000000c0000
Mft2 Start Lcn : 0x0000000000000002
Mft Zone Start : 0x0000000004f53680
Mft Zone End : 0x0000000004f5fea0
MFT Zone Size : 200.13 MB
Max Device Trim Extent Count : 256
Max Device Trim Byte Count : 0xffffffff
Max Volume Trim Extent Count : 62
Max Volume Trim Byte Count : 0x40000000
Resource Manager Identifier : 6760C3CC-D86B-4B5A-9FF9-C44539F59F48Look for the Bytes Per Cluster value.
In this example, it is 4096 (4 KB), which is the default allocation unit size.
Repeat the same command for each drive you want to check.
Conclusion
As always, if you have any questions or know a better method, feel free to leave a comment below. Thanks for reading, and see you next time!
