Before posting, and to avoid disappointment, please read the following:

  • This forum is not for 2BrightSparks to provide technical support. It's primarily for users to help other users. Do not expect 2BrightSparks to answer any question posted to this forum.
  • If you find a bug in any of our software, please submit a support ticket. It does not matter if you are using our freeware, a beta version or you haven't yet purchased the software. We want to know about any and all bugs so we can fix them as soon as possible. We usually need more information and details from you to reproduce bugs and that is better done via a support ticket and not this forum.

Backing up very large files - make a delta?

For technical support visit
Post Reply
Posts: 2
Joined: Thu Oct 04, 2018 12:37 pm

Backing up very large files - make a delta?

Post by simonjshaw »

I have seen some passing references to this, but apologise if I haven't found a previous answer - please redirect me if so.

Backing up the Changed portion of a large file

When there are very large files to back up, which change regularly but only slightly (for instance, .pst archives from outlook email) we would like only to backup the portion of the file which has changed. Otherwise it just takes ages, takes up too much space and causes trouble with multiple versions. Backup target is Amazon S3 in case that makes a difference.

I don't think SyncBack can do large file deltas? Is that right?

So I think this requires a layer of functionality on top of SyncBack, to manage deltas.
i.e. to ensure a backup of the original complete file, but thereafter only to create and back up a delta on each backup iteration.

I have done some experiments with xdelta which would seem to work in principle, according to this algorithm:
precondition: exclude relevant files from the backup profile
- before the backup, find the relevant files (e.g. *.pst in the source)
- for each one, if a "base" image does not exist in a named (xdelta) subfolder, then create it (so it gets backed up)
- otherwise, create a "delta" file from the base file and the current file, storing that in the subfolder (it gets backed up)

If I'm barking up entirely the wrong tree, pls tell me so, otherwise read on...

So I need to execute a script to do this before the backup, but I'm in a pickle about the required quote marks for pathnames with spaces.
Am I supposed to use \" or "" ? Neither seems to work properly.
Can someone have a look at this and either correct it or give me a good alternative to the whole method?

@echo off
cd \
for /r %%i in (*.pst) do (
if exist %%~pi\xdelta\%%~nxi.base (
"c:\program files\xdelta\xdelta3.exe" -e -q -s \"%%~pi\xdelta\%%~nxi.base\" \"%%i"" \"%%~pi\xdelta\\"
echo %%~nxi delta created
) else (
mkdir \"%%~pi\xdelta\"
copy /B /Y \"%%i\" \"%%~pi\xdelta\%%~nxi.base\"
echo %%~nxi base file created

Any help gratefully appreciated.
Posts: 1023
Joined: Mon Apr 13, 2015 6:22 am

Re: Backing up very large files - make a delta?

Post by Swapna »


Delta copy (or Block syncing) is not supported in SyncBack. This feature is in our to-do-list, but there is no ETA on when it will be available. You can refer to this forum post:


Thank you for your understanding.   
Posts: 40
Joined: Mon Sep 12, 2016 5:27 pm

Re: Backing up very large files - make a delta?

Post by Engztrom »

It would be nice if you could give this feature some priority!
(Stupid Outlook changes all my .pst file timestamps when it is started, even untouched archive files,
so approximately 90% of my backup time goes to backup unchanged .pst files to the cloud...)
Post Reply