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Large File Uploads

The Large File Upload upgrade allows the upload of large files up to 2GB on the Castor platform. By adding this feature, the maximum file upload size will be upgraded from the standard limit of 5MB to 2GB per file. The increased file size is designed for studies that require the upload of large files, including:

  • Medical imaging, including X-Ray, CT, MRI
  • Pathological/microscopy imaging
  • High resolution photography
  • Videos
  • Zip files

Getting started

To enable the upload of large files, the feature must be requested and enabled for your study by the Castor support team. This is a premium feature and thus is associated with additional costs. 

Uploading Large Files

With Large File Upload, you can use the same Upload File fields used for standard file uploads or import the files using the API. For more information about the field, see the article: The 'Upload File' field. The Castor API documentation can be found here -

Fair Usage

There is no limit, however we have a fair use policy based on a maximum upload of 100GB/month data transfer (upload and download). For storage needs that exceed 1.2 terabytes/year, we can provide a customized quote.

File Hosting

Large files are stored on Google Cloud hosted servers by default - other options can be arranged subject to additional costs e.g. Azure, AWS or custom options. For a complete list of possible regions, see the cloud provider locations:

For studies with large file upload enabled, costs apply if you wish to continue storing the files after the study ends.  This will be a custom charge depending on the amount and your intended usage (data transfer costs). 


File storage is encrypted and the encryption keys are stored in a different location to the files, for security reasons. All data passes through Castor servers, where it is encrypted, before going to the cloud provider. File names and extensions are also removed before being uploaded. The cloud provider does not have access to the unencrypted data.


Due to the size of the files, the 'Uploaded files to zip file' option cannot be used to bulk download at this time. As seen with the 'Upload file' field, it’s only possible to preview certain image file types such as pdf and image files. In the future, an integration with DICOM viewers will be available for imaging files.

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  1. Castor Support Team

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