Backing up very large files - make a delta?

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Backing up very large files - make a delta?

Post by simonjshaw » Thu Nov 29, 2018 2:17 pm

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.

2BrightSparks Staff
2BrightSparks Staff
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Re: Backing up very large files - make a delta?

Post by Swapna » Fri Nov 30, 2018 1:08 am


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: 36
Joined: Mon Sep 12, 2016 5:27 pm

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

Post by Engztrom » Wed Jan 02, 2019 9:17 am

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...)

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