How to find the NTFS format allocation unit size in Windows?
The allocation unit size is the block size on your hard drive when it is formatted using NTFS. The default is 4096 bytes, lower numbers can save a bit of space at the cost of speed, and larger units can provide a bit faster access. Generally, smaller external drives should be left at the default allocation unit size, and drives larger than 1TB can benefit slightly from bumping it to 8192, or even 16384 if you are only storing large files.
It is sometimes useful to find the allocation unit size of already formatted drives. In newer Windows versions, start PowerShell, and simply copy, or type the following:
Get-Volume | Format-Table DriveLetter, FileSystemLabel, AllocationUnitSize
You will be presented with a list of drives, their corresponding labels and allocation unit sizes. Internal hard drives, DVD-ROMs, and external USB/eSATA drives are all listed.