Is there any program where, if I have my computer connected to my external hard drive and download something to the computer's internal hard drive, it then mirrors this out to the external hard drive? I am looking for something as transparent as RAID.

  • Ideally, this process would be entirely automated.
  • Open source software and linux compatibility would be a plus.
  • If it requires either a batch script or shell script I am perfectly fine with that.
  • Synchronizes in real time or, if that's not possible, at least in intervals

The primary goal simply is to duplicate my data onto external media in real time at best and something like timed intervals at worse. Also, in backing data up I wouldn't want to use a script that just completely overwrites the mirror drive. I want it to realize where changes were made and as such change the mirrored system to reflect these changes.

  • 3
    Welcome to Software Recommendations. This question still needs more details in order to have a chance of getting answered. For example, which operating system(s) should this software run on? What is your budget for such a program? Should it be fully automated or could the user launch the command? etc... For more information on how to improve your question, please read this FAQ on what is required for a question to contain enough information
    – Tymric
    Commented Dec 5, 2014 at 8:24
  • I've to second Timmy in all points. // One raw idea of a matching product is git-annex, which probably could be configured that way.
    – Izzy
    Commented Dec 5, 2014 at 9:45
  • This question seems straightforward to me... SecondCopy fits the description except that it gets no bonus points for being open source or linux, both of which it isn't. I use second copy pretty much the way described by the poster.
    – ycomp
    Commented Dec 5, 2014 at 19:52
  • ah, I see.. it's unclear what OS is needed.
    – ycomp
    Commented Dec 5, 2014 at 19:52

3 Answers 3


Second Copy from Centered Systems will do exactly what you want.

It will create a mirror copy of any data you specify. It is very flexible.

It can be obtained from www.secondcopy.com

Good luck!

  • 1
    yeah Second Copy is great. Especially now that Microsoft removed File Versions in an attempt to dumb things down. File History just doesn't do the job Second Copy does, it only takes Snapshots at a minimum of 1 hour. Snapshots are good for general backup but sometimes you want to have a copy of each 'n' number of most recent file versions. But anyhow Second Copy is highly configurable, so you most likely you can get it do what you want.
    – ycomp
    Commented Dec 5, 2014 at 19:46

git-annex might be a good candidate here. You can think of it as a kind of "open-source Dropbox and more". It can work locally, via network, with online media.

At a first look it might seem a bit "confusing and hard to set up" – but luckily there's git-annex assistant which makes things easy (just look for that at Youtube for some nice presentations). For your case, I'd recommend using that to set up two "annexes": One is the download directory on your local harddisk, and the other is your "external drive". Now, everything you drop in one place, is easily "known" on the other – though by default not "physically there". For the latter, you simply declare the entire "local harddisk annex" as "preferred content" in your "external annex" – which then would take care to automatically make the content itself available there (instead of just the metadata).

make a repo another repo
git-annex assistant guides you through the setup process in easy steps (click images for larger variants)

The entire process is not usually triggered immediately, but might have a short delay (the daemon checks in intervals AFAIK). git-annex works fine on Linux and Android (not sure about other systems, but if I remember correctly, also on Mac and Windows).

git-annex demo
a git-annex assistant demo screen: matches your situation with the USB stick :)

Some additional links which might prove useful:


You don't mention that it must be free. I would highly recommend paying US $19.99 for a personal version of Bvckup 2. I did, and I have never regretted it.

I did a lot of research before choosing it, and what convinced me was partly that it supports VSS, so that it can synch files which are in use, and, especially, the speed, it wins every test because it uses delta copying:

Reduce the amount of data being moved around by copying modified parts of files only. This speeds things up, in many cases dramatically.

enter image description here.

There is a 5 start review of it at PC World.

If you don't want to spend, or just want to try it out, the last beta, which is quite recent, is available here.

If you still don't like Bvckup2, then I can highly recommend FreeFileSynch, which I previously used. See my long answers to this SR question, and this one and this one too.

To save you the trouble of clicking those links, here is the feature list:

Key Features

Detect moved and renamed files and folders
Copy locked files (Volume Shadow Copy Service)
Detect conflicts and propagate deletions
Binary file comparison
Configure handling of Symbolic Links
Automate sync as a batch job
Process multiple folder pairs
Comprehensive and detailed error reporting
Copy NTFS extended attributes (compressed, encrypted, sparse)
Copy NTFS security permissions
Support long file paths with more than 260 characters
Fail-safe file copy
Cross-platform: Windows, Linux, Mac OS X
Expand environment variables like %USERPROFILE%
Access variable drive letters by volume name (USB sticks)
Native 64-bit support
Keep versions of deleted/updated files
Prevent disc space bottlenecks via optimal sync sequence
Full Unicode support
Highly optimized runtime performance
Include/exclude files via filter
FreeFileSync portable and local installation available
Handle daylight saving time changes on FAT/FAT32
Use macros %time%, %date%, et al. for recurring backups
Case-sensitive synchronization
Built-in locking: serialize multiple jobs running against the same network share 

Supported Operating Systems

Microsoft Windows Microsoft Windows FreeFileSync runs natively on all 32 and 64-bit Windows versions:

Windows 10
Windows 8.1
Windows 8
Windows 7
Windows Vista
Windows XP
Windows 2000

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