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Formatting a large external drive as exFAT (allocation unit size question)

Anonymous
2014-10-14T09:53:37+00:00

I just purchased a new 3TB external hard drive for my desktop and wanted to format it to exFAT so I could move it back and forth between my different operating systems easily, but I'm running into trouble with the file allocation size unit selections. On smaller drives it seems I can set it to as low as 512 bytes, but on this drive the smallest option I can see is 256 kilobytes.  If I format it to NTFS however, I can set it as low as 4096 bytes. In fact, the largest I can set it to in NTFS is 64 kilobytes, so 256 seems like way too much. Does anyone know why this is and if there is a way to get it smaller? Thanks a lot!

Windows for home | Previous Windows versions | Files, folders, and storage

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  1. Anonymous
    2014-10-15T23:37:39+00:00

    If anyone has this problem later, I found the solution. If you run cmd as administrator, you can format the drive and specify the cluster size manually by typing:

    Format X: /A:#### /Q /FS:ExFAT

    Where X is the letter of the drive you want to format, #### is the size you want the cluster to be. /Q is if you want to do a quick format, and /FS: specifies the filesystem type. In this case I wrote "Format I: /A:4096 /Q /FS:ExFAT" but you can set the allocation unit size to as low as 512 (bytes) or as high as 32M (megabytes). Type Format /? for more help.

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