Allocation unit size when formatting USB flash drive


  1. VinceB
    Posts : 128
    Windows 10 Home x64 vers. 21H1; Build 19043.1889
       New #1

    Allocation unit size when formatting USB flash drive



    Hi:

    I am currently involved with transferring music MP3 files to a 32-GB thumb drive and have needed to reformat the thumb drive several times during the troubleshooting process that I am dealing with. I do not know how to make an intelligent choice for the Allocation unit size, and why. Also, I want to learn how to set/reset the File system (Default) settings. Presently, the File system is showing as FAT32 (Default) and the Allocation unit size is showing as 16 kilobytes (cluster size). Are those selections appropriate for the task at hand?

    Is there a tutorial/blog available that would provide insight to those formatting selections?

    TIA.
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  3. Berton
    Posts : 14,005
    Win10 Pro and Home, Win11 Pro and Home, Win7, Linux Mint
       New #2

    When I've had to repartition/reformat USB Thumb drives it usually is as FAT32 and the cluster size shown as 4096KB. It would be nice is all files of a type were exactly the same size but since they aren't more than 1 cluster is needed to hold those parts, fragmentation occurs when all the clusters for one file are scattered across the drive, not always contiguous to each of the others. If the cluster size is too small there's lots of pieces and if too large there may be too much wasted space [called slack]. On an HDD/Hard Disk Drive those clusters have to be read and written, takes longer and why defragmentation helped mightily in performance.
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  4. Paul Black
    Posts : 18,044
    Win 10 Pro 64-bit v1909 - Build 18363 Custom ISO Install
       New #3

    Hello @VinceB,

    VinceB said:
    I am currently involved with transferring music MP3 files to a 32-GB thumb drive and have needed to reformat the thumb drive several times during the troubleshooting process that I am dealing with.

    Normally, on a USB, if ALL the individual files are less than 4 GB, then FAT32 will suffice.

    Have a look at this => How to Format a Disk or Drive in Windows 10

    [1] When you say that you are having problems, what exactly do you mean?
    [2] Are there ANY error mesages?
    [3] What exactly is wrong?


    Another option is . . .

    DISKPART - Clean AND Format:

    [1] Press the Win + X keys together > Command Prompt (Admin).
    [2] Type EACH command below Individually into the Administrator: Command Prompt Window > Enter.

    disk part
    list disk
    select disk # Where # is the USB Disk Number.
    clean This will ERASE EVERYTHING from the USB.
    create partition primary
    format fs=NTFS quick Change to format fs=fat32 quick for FAT32.
    exit
    exit


    NOTE:

    If the FILES that will be used are NO BIGGER than 4GB, then you may want to Format the USBs as FAT32.


    I hope this helps.
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  6. VinceB
    Posts : 128
    Windows 10 Home x64 vers. 21H1; Build 19043.1889
    Thread Starter
       New #4

    Paul Black said:
    Hello @VinceB,
    .....
    [1] When you say that you are having problems, what exactly do you mean?
    [2] Are there ANY error mesages?
    [3] What exactly is wrong?
    .....
    I hope this helps.
    @Paul Black: Please see my "MP3 music syncing with WMP" thread in software-apps forum, originated 1 week ago.

    I have been reformatting the thumb drive each time I test for a solution, and thought that I should have/needed a better understanding of the formatting options offered.

    I believe the MP3 files are in the 3- to 9-MB range per song/file.
    Allocation unit size when formatting USB flash drive Attached Files
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  7. Megahertz
    Posts : 6,299
    Windows 11 Pro - Windows 7 HP - Lubuntu
       New #5

    As Berton already mentioned, flash drives till 32G are normally Fat32 with allocation unit size of 4096 bytes. If you don't have any file bigger than 4G, there should be no issues.

    What kind of error made you needed to reformat the thumb drive several times?
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  8. VinceB
    Posts : 128
    Windows 10 Home x64 vers. 21H1; Build 19043.1889
    Thread Starter
       New #6

    Megahertz said:
    As Berton already mentioned, flash drives till 32G are normally Fat32 with allocation unit size of 4096 bytes. If you don't have any file bigger than 4G, there should be no issues.

    What kind of error made you needed to reformat the thumb drive several times?
    I haven't made myself clear. In this situation, I ran into problem that the MP3 files did not play in my 2013 Accord's audio system. I think now it may be a matter of too many files (~630 MP3 files, initially) on the drive (a HONDA compatibility problem). So, I would reformat the thumb drive and then retry with fewer MP3 files placed on the thumb drive. It was NOT due to any error, etc. Drive reformatted prior to transferring a different batch of MP3s on the device.

    I have read that the allocation size is auto detected ??
    It is a 32GB thumb drive, but I do not see a 4096 bytes option. I see 8k, 16k, 32k and 64k-bytes.
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  9. Paul Black
    Posts : 18,044
    Win 10 Pro 64-bit v1909 - Build 18363 Custom ISO Install
       New #7

    Hello @VinceB,

    VinceB said:
    It is a 32GB thumb drive, but I do not see a 4096 bytes option. I see 8k, 16k, 32k and 64k-bytes.

    The 4096 bytes is for NTFS.

    I think the confusion here is the File Allocation Unit Size used between NTFS and FAT32. Here is some information that will help explain in more detail . . .

    > What Allocation Unit Size To Use When Formatting A USB Fash Drive In FAT32?
    > File Allocation Table
    > What Allocation Unit Size Should I Use for FAT32?

    I hope this helps.
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  10. Megahertz
    Posts : 6,299
    Windows 11 Pro - Windows 7 HP - Lubuntu
       New #8

    Paul Black said:
    Hello @VinceB,
    The 4096 bytes is for NTFS.
    Paul, all my USB flash drives are Fat32 with allocation unit size of 4096 bytes.
    Not sure but bigger allocation units only make sense on drives bigger than 32G
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