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Large File Upload Fails in FileCloud Sync with Amazon S3 Due to Multipart Upload Limit

Original Question or Issue:

 Large file uploads to Amazon S3 fail when using FileCloud Sync, while the same files upload successfully through the FileCloud Web UI. 

Environment:

  • Product - FileCloud Sync
  • Version - 23.253
  • Platform - Windows, Linux

Steps to Reproduce:

  • Configure Amazon S3 as the Managed Storage.
  • Use FileCloud Sync to upload a very large file (e.g., 430 GB or larger).
  • Observe that the upload fails after exceeding the Amazon S3 multipart upload limit.
  • Upload the same file through the FileCloud Web UI.
  • Observe that the upload succeeds when the Managed Storage Chunk Upload Size is configured appropriately.

Error or Log Message:

CLFC-50018 - Uploading of the file failed

Defect or Enhancement Number:

FCL-11564

Cause:

FileCloud Sync uses a fixed multipart upload chunk size of 20 MB and does not honor the Managed Storage → Chunk Upload Size configured in the Admin Portal. For very large files, this results in more than 10,000 multipart upload parts, exceeding Amazon S3's maximum supported limit. In contrast, the Web UI uses the server-configured chunk upload size, allowing larger uploads to remain within the multipart upload limit.

Resolution or Workaround:

  • Increase Admin Portal → Settings → Storage → Managed Storage → Chunk Upload Size (e.g., 50 MB or higher as appropriate).
  • Upload large files using the FileCloud User Portal (Web UI) instead of FileCloud Sync.
  • For synchronization going forward, migrate from FileCloud Sync to FileCloud Desktop, as FileCloud Sync is being sunset and is no longer under active development.

Notes:

  • The Managed Storage Chunk Upload Size setting only applies to uploads performed through the Web UI.
  • FileCloud Sync always uses a fixed 20 MB chunk size.
  • A successful upload of a 1.15 TB file through the Web UI confirms that the FileCloud server and Amazon S3 storage support very large files when the multipart upload remains within Amazon S3's 10,000-part limit.