I can transfer folders in Grsync and it works really good, including files that are deleted when I check 'delete on destination,' but when I do that it's always copying the whole file. Is there a way to do the incremental saving, where it only copies the changes (additions and deletions) and doesn't have to copy the entire thing? Thanks.

Just read the manual of rsync.

Rsync always copies only changed files by reading the last write access in the header of the file.

I don't know about grsync, but in regular rsync there's an option called inplace. I think that's what you're looking for. Basically, when transfering a file that's been changed, it adds, truncates or updates the file based on checksums of parts of the file. So if you have just changed a little bit, not very muuch is transfered.

But for safety reasons, by default, it does it on a copy of the file. It's to prevent against corrupting the file if something fails while it's working. If you add --inplace, you disable that safety system, and simple file changes become a lot faster.

The rsync manual states (in its description of the -W, --whole-file option) that whole-file copying is the default behavior for transfers between local paths.

You can enable "delta-transmission" by the --no-W switch as shown below. In this example, I transferred two files of approximately 64 MB each. In file1, I had changed a single 64K block near the middle. In file2, I had appended a 64K block to the end.
Edit: Delta transmission does not necessarily speed up the transfer. It does less disk IO but has to do more hashing. Here on my old laptop, the speed was about the same, 2.45s real time for the whole-file transfer, and 2.29s for the delta transfer.

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Thanks everyone. I'm a little psyched out by the advice though. Seems grysnc is quite a bit more sophisticated than I thought. But let me get one thing straight. If I check the "delete on destination" square (see screenshot), that means whatever I have added or subtracted from the source will be transferred to the destination, right?

And since, like Berryllos said, the incremental transferring really doesn't speed things up I see no real advantage anyway.

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Whatever you have added or modified will be transferred, regardless of whether you check "delete on destination."

If you check that box, files that have been deleted on the source will then be deleted on the destination.

That depends on the speed of the drives you are using. If the drive I/O is slow, you could gain a lot by transferring only the changed blocks. If you are backing up to USB flash drives, it might also extend the life of the flash memory by eliminating unnecessary write cycles.

By the way, in grsync I do not see a checkbox for that, but you can add it in the "Additional options" text box (under the Advanced options tab). You would add the following code, separated by spaces from any other options that appear there:

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Nice explanation. Thanks.

I wasn't quite sure what you were referring to by "that" in the sentence "By the way, in grsync I do not see a checkbox for that..."

Could you please clarify?

And so I would just do it like it is in the screenshot?

Thanks.

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Yes, the screenshot shows how to correctly add the --no-W option, which enables "delta-transmission" mode, which only copies the changes and doesn't have to copy the whole file.

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Thanks Beryllos. Appreciate the response. I will definitely experiment with that. I think that is exactly what I've been looking for.

Beryllos, one more question. When I do the delta-transmission do I have the "Delete on destination" box checked? Thanks.

Whether you check the "Delete on destination" box or you don't, that doesn't affect the delta-transmission functionality.

"Delete on destination" tells rsync to delete files from the receiving side if they do not exist on the sending side. This is great if you want the receiving side to correspond exactly to the sending side. It will copy any new files, update any modified files, and delete any deleted files. It will also delete any unrelated files that happen to be in the receiving directory.

If you don't check the "Delete on destination" box, it will still copy any new files and update any modified files, but it will not delete anything on the receiving side. This might be useful if you wanted, for example, to add and update files to a directory that contained additional files from somewhere else.

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Amazing. You explain things so well. (I often have an incredibly hard time understanding a lot of the advice given, but I understand yours so easily.) Thanks so much. I really feel I have a good grasp of this now.