A little mishap happened earlier today and i am thinking i should have a copy of my external harddrive since 10% of it is very valuable. What is the best solution to keep two external harddrive in sync? i'll probably use one as regular and maybe use the other only to copy data. The easiest way to keep it in sync is to clear one drive and copy the other but 1T of data will take a long time.

Whats a good existing app that will keep them in sync? freeware preferred.

4 Answers 4


rsync and maybe rdiff-backup.

On Windows - robocopy (comes with Vista).

  • it looks like robocopy C:\src C:\dst /mir /copyall will do the trick (but requires admin rights to access/set the security attr with copyall) -edit- to note mir will delete files that dont exist on src like i wanted.
    – user3109
    May 14, 2010 at 21:28
  • There are a few more flags you might want to look at. For example /b allows you to copy directories even if you're not the owner, as long as you run robocopy as an admin. (I have a bunch of user folders -- Desktop, Documents, etc. -- from previous Windows installations on my external drives, and it's impossible to access them without either using that flag, or painfully changing the owner and permissions first.) You might also want to exclude junction points and symbolic links, which will get traversed unless you explicitly say otherwise.
    – Archagon
    Dec 10, 2012 at 22:17

If you're in Windows, you can use Synctoy. Very easy to use IMO.

  • I like this because it's so easy to use. Dec 4, 2011 at 21:49

This article compares FreeFileSync and SyncToy

Although they roughly perform the same functions, FreeFileSync had an edge over SyncToy in Performance, portability and overall has slightly more features. One advantage in particular of FreeFileSync over SyncToy is the ability to copy locked (ie open) files (SyncToy can’t copy locked files)


When I have to use Windows or when setting up for Windows users.

For hourly and daily unattended sync I really like PtReplicator which is a really easy, powerful, fast, and free.

When I am doing manual syncs, or have an external that I want to have the software and settings available on the external disk when I plug it in I use Toucan Portable. I love this one because I have several different drives for specific uses.

When I'm on my Ubuntu boxes I agree with the Grsync suggestion.

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