VSS in Windows?

phni     Aug 6 5:02AM 2016 GUI

Does the windows version offer support for Shadow Copies/VSS ?

Arq seems to be a main competitor. It's has been a proven solution for years. What do you see as the main benefit of duplicacy?

gchen    Aug 6 7:44PM 2016

Yes, you need to run the program as administrator to enable the option.

What distinguishes Duplicacy from other tools including Arq is the ability to do cross-computer deduplication. If you need to back up multiple computers, Duplicacy can use a single storage as the backup destination, so that identical files or blocks on different computers can be mapped to the same chunks. This reduces the storage space and speeds up the backup process (there is no need to upload a chunk that has already been uploaded by another computer).

Here is a real-world example that shows the effectiveness of cross-computer deduplication. Our Duplicacy code base (which also contains other projects such as Acrosync) resides on multiple computers (Windows and Mac), and I use Duplicacy for hourly backups. The duplicacy check -stats command lists the total storage space each repository takes and how much of it is not shared with others:

Snapshot duplicacy-win10 all revisions: 1,467M total chunk bytes, 482,815K unique chunk bytes
Snapshot duplicacy-mac all revisions: 2,673M total chunk bytes, 993,411K unique chunk bytes
Snapshot duplicacy-xps8700 all revisions: 1,040M total chunk bytes, 54,795K unique chunk bytes
Snapshot duplicacy-mac-mini all revisions: 1,834M total chunk bytes, 134,437K unique chunk bytes
Snapshot duplicacy-win7 all revisions: 4,416M total chunk bytes, 4,044M unique chunk bytes

As you can see, cross-computer deduplication almost halves the total storage space required to backup these repositories. The saving would have been greater had there been more computers. I don't think Arq or any other tool can do the same, because this is only made possible by Lock-Free Deduplication, an idea I came up with last year which inspired me to develop Duplicacy.

T3h Ub3r K1tten    Aug 7 10:53PM 2016

When I run as administrator on Windows Server 2012, the VSS checkbox is grayed out. Anything I'm missing?

gchen    Aug 8 9:09AM 2016

You may need to log in with an administrator account.

Ovidiu    Aug 11 2:21AM 2016

Hi, thanks for clarifying this BUT I only realized VSS is not selectable after setting up my backup, now if I run duplicacy as administrator all that is gone and I have to set it up again. That feels quite useless, after all I am still running it as the same user? edit realized that selecting the same repository, will automatically load all settings I had previously made.

Jeremy    Jun 23 10:50AM 2017

Is it looking at the actual account name?

When I login as a domain admin user, which is part of the local Administrators group, the VSS checkbox is grayed out. If I login as an account with the literal name "Administrator", it allows me to select that box.

It seems that it would be better to check the user's actual permission, right?

Thank you!


gchen    Jun 23 3:19PM 2017

No, we don't look at the account name. We check if the process is run with elevated privileges, and if it does, then the checkbox will be enabled.

Jeremy    Jun 26 12:48PM 2017

Unfortunately, even if I right-click and choose "Run as administrator", I am still unable to select the VSS box.

In addition, I cannot even load the repository previously created via an admin-level command prompt.

The error says "The Duplicacy service may be backing up the same repository. You need to run with administrator privileges to manage the service." (This is after I right-click and choose "Run as administrator", and click "Yes" to the generic Windows UAC prompt)

gchen    Jun 26 2:21PM 2017

It looks like you didn't exit the current Duplicacy instance. Right click the system tray icon and select Quit. Otherwise Duplicacy will stay in the background if you just close the windows.

The error was because the repository path stored under HKCU/Software/Duplicacy/Repository is the same as HKLM/Software/Duplicacy/Repository, so the Duplicacy instance without the elevated privileges can't tell if the service is backing up the same repository. Removing HKCU/Software/Duplicacy/Repository or changing it to a different value should get ride of the error message.

Jeremy    Jun 27 2:13PM 2017

Ah-ha! Closing it from the system tray did the trick. Thank you!

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