Mirror vs 2-way Synchronization

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Joined: 24 Sep 2018

Paul

I would appreciate being given some help in understanding how to use the backup program and, more specifically, whether the program allows me to do the type of backup I want to do.

One of the reasons for asking for help is that, unless I missed them, some of my questions aren't addressed either in the online manual or in the videos.

For example, I don't know how *mirror* may differ from *2-way" synchronization and if one or both does the following:

I don't know if a file that is deleted in the Source Disk will also be deleted in the Target Disk (if it's there) or if a file in the Target Disk will be updated with the same file having the same name but a different time stamp in the Source Disk.

It would help if I begin by stating what I do not want.

I do not want to do a differential backup or an incremental backup. And, I do not want to back anything up to the cloud.

The purpose of what I want to do is backup data (files/folders that I create). When I restore, it would be to a new computer.

I want the following features:

(1) The Source disk and the Target disk are always identical.

(2) If a file (or a folder) is *deleted* from the Source Disk, it is also deleted from the Target Disk during the next backup.

(3) If a file (or a folder) is *added* to the Source Disk, it is also added to the Target Disk during the next backup.

(Note that the additions/deletions above in (2) and (3) are NOT done through differential backups or incremental backups. After the next backup, the Source and Target are identical.)

(4) Once the first full backup is done, all subsequent backups take much less time because the only changes needed to the Target Disk are changes that were previously made to the Source Disk.

(5) I do not want to make a mirror image of the entire Source Disk that includes programs, Windows, or anything else than data files.

As mentioned above, I don't know how to set up a backup scheme whereby: (a) a file that is deleted in the Source Disk will also be deleted in the Target Disk (if it's there) or (b) a file in the Target Disk will be updated with the same file having the same name but a different time stamp in the Source Disk. I want the Target Disk to be identical to the Source Disk after a backup is done.

Thank you for your help.

Paul
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Joined: 22 Aug 2012

Plerry

As you describe your needs, you should use the Mirror variant.
To the extent that you do not exclude items from the sync, this will result in the Target containing an exact file level copy of the Source after an FreeFileSync (FFS) sync.
The only limitation is that folders deleted from the Source, but pre-existing on the Target will not be deleted from the Target (any files in such folders will get deleted).

FFS is a file-level sync-tool; there are no incremental/differential sync-actions.
The Update sync variant does the same as the Mirror variant, but leaves files that pre-exist in the Target but do not or no longer exist in the Source intact.
The TwoWay variant (like the name suggests) provides a bi-directional sync between the left and right base location (Source and Target are improper terms in this context), and is useful if files are created, changed and/or deleted in both locations. A Two-Way sync in which files only get created, changed and/or deleted on one side, acts essentially the same as a Mirror sync.

However:
You use the word "backup" several times and even explicitly state:
"I want the Target Disk to be identical to the Source Disk after a backup is done. "
An identical copy of the Source on the Target is just that: a copy of the latest status.
Such copy can form part of a backup, but is not a backup.
A backup is more than just a copy; described in a funny way here .
(and please forgive them the commercial twist at the end).
FFS can also partially help you there when using Versioning as your Delete Files sync-setting (F8).
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Joined: 24 Sep 2018

Paul

Plerry,

Thank you for your reply. It was extremely helpful. It made me aware of the fact that I'm too much of a newbie and lack a comprehensive understanding of much of the nomenclature used on this and similar sites.

It's clear to me now that FreeFileSync will accomplish much of what I need.

Before posting this reply, I studied the site once again. To make sure that my understanding is good, I hope you will answer a few more questions.

Let's assume that I perform a synchronization as follows:

The *one* folder I want to back up contains 10 individual files and also contains 10 subfolders each one containing 10 individual files.

A *mirror* synchronization is done to an external hard drive.

After:

(a) a file is changed in one of the *subfolders* on the Source Drive
(b) a file is deleted in one of the *subfolders* on the Source Drive
(c) a file is added to one of the *subfolders* on the Source Drive
(d) one of the *subfolders* on the Source Drive is deleted
(e) a new *subfolder* is added on the Source Drive

Am I correct in assuming the following?

(a) if a file is changed in one of the *subfolders* on the Source Drive - and I set the "Comparison Settings" to File Time and Size - then the file that is on the Source Drive will overwrite the file on the Target Drive.
https://freefilesync.org/manual.php?topic=comparison-settings

(b) if a file is deleted in one of the *subfolders* on the Source Drive, then it will also be deleted on the Target Drive.

(c) if a file is added to one of the *subfolders* on the Source Drive, then it will also be added to the Target Drive.

However, (d) if one of the *subfolders* on the Source Drive is deleted, it will NOT be deleted on the Target Drive but that subfolder will be empty (will not contain any files).

(e) if a new *subfolder* is added on the Source Drive, it will also be added to the Target Drive.

Last, I assume that after the fist mirror synchronization, all subsequent mirror synchronizations will consume much less time because it will not involve the transfer and overwriting of indentical files and folders already on the Target Disk.

Your first reply to me pointed out the importance of organizing the directory tree before the first mirror synchronization (i.e., once on the Target Drive, folders and subfolders will not be deleted if they are deleted on the Source Disk; only the file contents are deleted).

I think I can work with that limitation because it's far more likely that I will create far more many folders than delete folders.

Again, thank your for your help.

Paul
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Joined: 22 Aug 2012

Plerry

As far as I know (I am not the developer and have not used FFS in all conceivable ways ...) your assumptions a), b) and c) are correct. As far as assumption d) is concerned, the assumption is correct if said subfolder (or any if its subfolders) contains at least one (non-excluded) file.
Look at it in this way: FreeFileSync is a file-sync program. It will gladly sync your (sub)folder structure, but essentially only as far as required to sync your files.

Note:
You wrote "A *mirror* synchronization is done to an external hard drive. After ..."
FFS does not run/sync automatically upon either of the mentioned changes, but only when told or triggered to run.
Running FFS can be manually, as a scheduled task, or launched by a program or script.
Particularly useful in this respect is RealTimeSync, that comes with the FreeFileSync installer.
RealTimeSync will monitor specified folders (+subfolders) for changes and upon detection of such changes launch a specified application, e.g. FFS.
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Joined: 24 Sep 2018

Paul

Plerry,

Thank you again. Your help has been over the top, and I am grateful to you. Hopefully, one day I will know enough to help others the way you helped me. I would have become very frustrated trying to learn what you taught me on my own, including by trial and error.

One last question, for clarification.

My previous question (d) pertained to the deletion of a *subfolder* on the Source Drive, and my assumption that the subfolder would NOT be deleted on the Target Drive (but that subfolder will be empty ... will not contain any files).

You wrote: "As far as assumption d) is concerned, the assumption is correct if said subfolder (or any if its subfolders) contains at least one (non-excluded) file."

To clarity - if I delete a subfolder on the Source Drive (which would include deleting all of its files and all of its subfolders), will FFS then delete the subfolder (and all of its files and subfolder)?

Regardless, FFS appears to be a very useful program that satisfies much or all what I need for the the "backup" of my data (I take your point that it is not a true backup program, but it does make my life a lot easier).

Paul
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Joined: 22 Aug 2012

Plerry

I mixed up your references d) and e)

- Your assumption d) was correct (in line with my reaction to your initial post)
- My earlier "As far as assumption d) is concerned, ..."
should have read "As far as assumption e) is concerned, ..."

Sorry for the confusion!
Posts: 61
Joined: 22 Apr 2018

markusoft

Look at it in this way: FreeFileSync is a file-sync program. It will gladly sync your (sub)folder structure, but essentially only as far as required to sync your files.

I think it creates the WHOLE structure first, and that to me is a problem
it shouldn't create the folder until it needs to be created

I can look at a cancelled job and it looks as if everything is copied
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Joined: 24 Sep 2018

Paul

Thanks for your comment, Markusoft ...

I think my initial confusion stemmed from not appreciating (understanding) the difference between a "backup" and "file synching".

What you wrote is of concern to me, as well ... but, if I understood what you wrote correctly, then my current understanding is somewhat different than yours.

You wrote that the folder structure is created first, and that it "shouldn't create the folder until it needs to be created." I'm not sure what you mean by that.

My understanding is that, yes ... all the folders (and their files) on the Source Disk are created (copied) on the Target Disk when the initial file-sync is performed.

After the first sync:

(a) Any new folder - containing files - that is created in the Source Disk will also be created (copied) on the Target Disk.

However, if the new folder on the Source Disk does not contain files, then it won't be created on the Target Disk.

(b) If files in a folder on the Source Disk are deleted, then they will also be deleted on the Target Disk.

If all the files are deleted, but the folder is *not* deleted, on the Source Disk .... then an empty folder *will* remain on the Target Disk.

However, if a folder that either does or does not contain files is deleted on the Source Disk, then an empty folder *will* remain on the Target Disk.

(c) If a folder on the Source Disk contains a file that was *updated* with new data, etc. but the name of that file was not changed, then this updated file will be copied to its corresponding folder on the Target Disk and, in the process, will overwrite (replace) the old file such that only the updated file will be found on the Source Disk.

Is the above your understanding (observation)?

I haven't done my first sync yet because I have at least a thousand folders on the Source Disk and need to reorganize the folder tree before the first sync.

Paul