Hi all! Since Crashplan is removing the P2P functionality I’m looking for an alternative, that is I’m looking to backup large files on one computer to another computer over the internet. Since size of data transfer is a concern I want to check how these three things work:
in-file delta transfers, only changed parts of large files are copied over the internet
versioning, I can setup to save indefinite versions of any file and the size of the backup will only grow by the size of the changes made
move and rename, the backup size will not grow and no sizeable data is transfered if large files are renamed or whole directory trees containing large files are renamed.
magnust, barring external factors (such as pre-Duplicati encryption) since Duplicati splits files up into smaller block sizes (check out the --blocksize parameter, not to be confused with --dblock-size) I believe what you should see is:
Only changes within a block are resent (so in a 100M file if 1byte is changed and your block-size is 100k, then a single 100k block will be sent. However, if 1k is changed the actually re-send amount could be anywhere between a single 100k file and 1,024 of them depending on how closely the 1k of changes aligns with individual blocks. Most likely you wouldn’t see more than 2 or 3 individual blocks being re-sent)
Yes, versioning works the way you describe except that the backup will increase in size not by the size of the changes made, by but by the size of the blocks necessary to “contain” the changes made (see answer #1).
Because of the blocks, moving / renaming files will not cause the file (blocks) to be re-uploaded, however there will still be some small increase in backup size due to recording the “versions” of file names / locations.
Oh, and I started this with “barring external factors” because if there’s some other process running on the machine that might, say, encrypt or compress files before Duplicati processes them then it’s POSSIBLE that a small 1k change could cause the entire file to “look” different (encryption often does this). Note that I doubt many (any?) people will really fall into this scenario but I THINK it’s possible (please correct me if I’m wrong) so thought I’d mention it.
If you really want to understand what will happen in these scenarios, check out this page.
magnust, glad to hear - let us know if you need any help getting things going!
If you feel my previous post fully answered your question feel free to give it a “like” (click on the heart icon) or even better use the checkmark icon to flag the topic as “resolved”. This helps others with similar questions know to this is a good thread to read!
I have found that Duplicati throws an error (might be a warning, cant remember) if you have a folder selected in the “choose which folders to backup” screen and at a later date you rename or delete one of the selected folders from disk without telling Duplicati that its gone.
I can’t remember if the error stops the backup process so nothing is backed up, or if it just skips the missing folder.
