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How does Dropbox upload huge files that changed only a small portion?

How does Dropbox upload huge files that changed only a small portion?

j7GUvseRjB
Explorer | Level 3
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I have a huge file in Dropbox. If I changed only a small portion, let's say 10 bytes from offset at 1GB position. Will Dropbox only upload the changed portion or upload the whole file again? Thanks.

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Rich
Super User II
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@j7GUvseRjB wrote:

I have a huge file in Dropbox. If I changed only a small portion, let's say 10 bytes from offset at 1GB position. Will Dropbox only upload the changed portion or upload the whole file again? Thanks.


It depends on how the saved file is written.

 

When Dropbox syncs your files, it first breaks them down into 4 MB chunks and then hashes each chunk. Dropbox then compares each hash to those that already exist in your account. Any that match are ignored and any that are different are uploaded. So, typically, if you have a large file already synced and you change just a few bytes, Dropbox will compare the entire file but only upload the chunks that have changed.

 

I said "it depends" earlier because there are cases where the entire file will be uploaded again. Such as while saving a file and the entire structure of the file changes, Dropbox will end up indexing and syncing the entire file even though you may have only made a minor change.

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Rich
Super User II
Go to solution

@j7GUvseRjB wrote:

I have a huge file in Dropbox. If I changed only a small portion, let's say 10 bytes from offset at 1GB position. Will Dropbox only upload the changed portion or upload the whole file again? Thanks.


It depends on how the saved file is written.

 

When Dropbox syncs your files, it first breaks them down into 4 MB chunks and then hashes each chunk. Dropbox then compares each hash to those that already exist in your account. Any that match are ignored and any that are different are uploaded. So, typically, if you have a large file already synced and you change just a few bytes, Dropbox will compare the entire file but only upload the chunks that have changed.

 

I said "it depends" earlier because there are cases where the entire file will be uploaded again. Such as while saving a file and the entire structure of the file changes, Dropbox will end up indexing and syncing the entire file even though you may have only made a minor change.

j7GUvseRjB
Explorer | Level 3
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Thanks for providing this info. So if I understand correctly, when I add a new byte to the beginning of the huge file, it will trigger a full upload, right?

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    j7GUvseRjB Explorer | Level 3
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    Rich Super User II
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