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There is a pdf file Data.pdf (~10 MB) stored in my Google Drive folder. I open the file in Adobe Reader, highlight a line and then save the file.
A re-sync will take place. I want to know whether the entire 10 MB of file will be synced or there exists a way by which changes can be synced by uploading only a part of the file?
The feature you are asking is called "Block-Level File Copying". With this feature, when you make a change to a file, rather than copying the entire file from your hard drive to the cloud server again, only the parts of the file that changed (called the delta) get sent.
A Google Drive sync cannot be partial. If a small change is made to a large file, it redoes the entire file rather than just the change. Google Drive isn’t capable of doing block-level file copies.
As far as I know, among the best-known cloud providers, only Dropbox has this feature for all file types. Dropbox partitions every single file it stores into 4MB blocks. Each block is hashed with SHA-256 and a list of these hashes gets stored in what’s called a “blocklist” for reference.
This feature is also shared by OneDrive, which however only supports it for Microsoft Office documents.
For more information and some benchmarks, see the article
Block-Level File Copying and the Cloud.
blocklist is considered for "Block-Level File Copying"; when a file is updated (a character is added at the beginning of the file), does Dropbox re-upload the complete file since the first block's hash will be change and it will also affect/change the hash of all the consequent blocks. @harrymc