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Question

Is it possible to change part_size of a chunked upload session ?

  • May 22, 2025
  • 6 replies
  • 102 views
C
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It seems like the Box Platform auto-determines the part_size of a chunk during a chunked upload session. Is it possible to modify or specify a desired part_size ?

 

For a trial I did, the part_size was 8Mb when I was uploading a 50Mb file; was 16Mb for a 200Mb file and 32Mb for a 1Gb file. For the network bandwidth that I'm using, a 32Mb chunk is just too large to handle and hence requires multiple resumes of the chunked uploader. A smaller chunk size would be ideal. But I don't see a way to specify it.

 

API reference:

"part_size" is one of the response parameters (https://developer.box.com/reference/resources/upload-session/#param-part_size) for a call to "Create upload session" (https://developer.box.com/reference/post-files-upload-sessions/)

 

    6 replies

    C
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    Hi , we currently do not support changing the part size when using chunked uploads. 

    C
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    Thanks for your response. I'd appreciate any other ideas you might have on how to handle file uploads in a slow network area ? I have to upload a file that is ~500Mb in size.

    When I tried tests with a 20Mb & 30 Mb files,
    * The effective upload rate is ~65kbps for the direct file uploader with the accelerator URL turned on.
    * The effective upload rate is ~50kbps for the chunked file uploader. But for these smaller sized files, the chunk size is 8Mb with which the network is able to complete upload of all the parts. With larger file sizes, the chunk size increases to 16Mb and 32Mb, and at this chunk size, there is a proxy error or some other network related errors that abort a chunk upload. Doesn't matter how many times I resume, the same thing happens.

    On the same computer, connected to the same slow network, I can open Box in the Web browser and am able to upload the 500Mb file. So I'm assuming that Box has other upload techniques that I'm not aware of.

    C
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     interesting. Would your users be able to use the UI elements to upload a file? As far as I know we don't use different part sizes in our app that we use in the API.

    C
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    Thanks . 

    I will check on the UI piece ... our original use-case was to run this without user interaction - will see if using the UI would be acceptable to the user group. I'm also checking if they can bump up their network bandwidth.

    I have clarity on the options available ... we can consider this thread as closed.

     

    BTW, thought you might be interested ... While digging into this, I think there is a possibility in the Python SDK for file digests to be incorrect when using the chunked uploader. I raised this issue at GitHub https://github.com/box/box-python-sdk/issues/495. This file digest issue is unrelated to the issue in this thread ... but something associated that I thought might be of interest.

    C
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    Tnx  . As for that Python issue, you listed it directly with the SDK team and they will look into it shortly.

    D
    • dylan3206
    • New Member
    • May 5, 2026

    Hello, is it possible yet to set the part_size to a custom value for chunked uploads when creating a chunked upload session? Or is this still unsupported and we need to use the value in the response to creating a session.

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