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    Allocation Unit Size/Cluster Size for 2TB exFAT Hard Drive

    Discussion in 'Hardware Components and Aftermarket Upgrades' started by codester, Jul 21, 2018.

  1. codester

    codester Notebook Consultant

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    Before I get into this, I do understand that a larger allocation unit size/cluster size is better for drives that will be storing larger files and read/write can be quicker as well; while a smaller size can save space, but read/write may not be as efficient. The main purpose of this drive will be to back up my files, and sometimes transfer them between my PC and Mac, so it will have many smaller files such as documents and photos, and larger files such as GoPro videos. Since this won't be used as a "working" drive, I'm not too concerned about speed.

    In the past (and on another 2TB drive) I have always stuck with the defaults Windows has (NTFS & 4096 byte allocation unit size). When using exFAT, Windows uses 512K (524,288 bytes) as the default allocation unit size. That is a big difference! I'm not sure if I like that. (How does Windows determine the default size for exFAT anyway?) The Mac will format it using 128K as the default, which is still a big difference.

    It appears that I could still specify 4096 bytes (not to be confused with 4096K) as the unit size if formatting it through DISKPART even though that option does not show when using the FILESYSTEMS command (or in the UI). Is that a bad idea to use 4096 bytes for exFAT - keeping it the size that I'm used to using? Should I just stick with the default, 512K...or go down to 128K?

    Any tips/suggestions would be greatly appreciated!
     
    Last edited: Jul 22, 2018
    codester, Jul 21, 2018
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  2. jclausius

    jclausius Notebook Virtuoso

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    512KB seems high... I believe 128K is default on exFat.

    See this for Windows defaults - https://support.microsoft.com/en-us/help/140365/default-cluster-size-for-ntfs-fat-and-exfat

     
    jclausius, Jul 22, 2018
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  3. codester

    codester Notebook Consultant

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    I came across that article too and saw that it didn't jive with my observations. It also doesn't list Windows 10, but I don't see why only Windows 10 would be different. If I manually format using 128K, and then issue the FILESYSTEMS command, it will list 128K as the default size. I'm not sure if has a similar behavior if I use a different size or not.
     
    codester, Jul 22, 2018
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  4. jclausius

    jclausius Notebook Virtuoso

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    Dunno what it would be different from the MS article. Is there an existing partition on the exFat drive? Or a setting you possibly used last?

    Regardless, 64KB or 128KB I think would fit just fine.
     
    jclausius, Jul 22, 2018
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