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I'll look at a couple of ways to back up to a computer located elsewhere, such as on a friend's or family member's computer, and discuss some of the issues of doing this.

I am trying to find a way to backup my computer automatically to a hard drive at another physical location (my parent's house). Is there a way to do this?

This is a pretty interesting scenario, and one that I personally used for some time while my wife had a retail business at a different location from my home. I would regularly backup in both directions - simultaneously achieving "off-site" backups for each.

But there were, and still are, limitations.

Today, there are a couple of approaches to peer-to-peer backup; I'll cover the most appropriate.

There are also a couple of things that people often think should work, and would work in concept, but they simply can't work for practical considerations.

Peer-to-Peer Backup

Do not confuse this kind of backing up with peer-to-peer file sharing, which we've heard so much about. This is completely unrelated, except for the concept of "peer".

"... peer-to-peer backups are not suitable for full system backups."

A peer is simply "someone like you". A co-worker at the same level as you is your peer. A student in the same class is your peer.

We use the same terminology when it comes to computers - two computers connected on a network that have no hierarchical relationship to them - one is not a server, for example - can be considered to be peers: on equal footing and with equal permissions and capabilities.

Peer-to-peer backup simply means that we take two computers and back up files from the first to the second and the second to the first.

While the two computers don't need to be in different locations from each other, we'll say that they are for the purposes of this discussion; by doing it this way, you'll get an off-site backup. Saved in a different location, this backup protects your data from things like your house burning down and destroying all your local machines and local backups.

Backing Up Your Data Versus Your Computer

We first need to rule out image backups, or backups of your entire computer. It's not that the techniques which we're talking about wouldn't work, they would. Perhaps even someday, they'll be practical, but today, they are not.

The problem is the speed of your internet connection and the sheer volume of data that you'd need to transfer to backup your entire system.

According to Akami, the average connection speed in the US is now 3.6 megabits per second.

Now, let's say you had 20 gigabytes used on your system, which is small, by today's standards. (Recall that a byte is 8 bits.)

Math then tells us that it would take over 12 hours to back up your entire machine under ideal circumstances.

Given that circumstances are rarely ideal, that many people have significantly less than a 3.6-megabit connection, and that most have significantly more than 20 gigabytes on their system, you can see that a full system backup would take days.

The result is that peer-to-peer backups are not suitable for full system backups.

On the other hand, they're great for data backups - the backups of only the data files on your machine - which typically don't add up to nearly as much.


I've talked about Dropbox before, but only in the context of sharing files with friends associated or simply across multiple machines.

But the same technology is also a great peer-to-peer backup solution.

When you install Dropbox and create a Dropbox account, it creates a folder which is then shared with all of the machines logged into that same Dropbox account. Update a file on machine A and it's magically updated on machine B whether that machine is across the room or the planet.

Sounds kinda like peer-to-peer backups, right?

You can also use it to share sub-folders with other specific Dropbox users. That way, you can use Dropbox for yourself, but also specify that a particular folder in your Dropbox (perhaps called "remote-backup") should be shared with your friend's Dropbox account. The same thing happens: updates within machine A's remote-backup folder are magically transferred to the remote-backup folder on your friend's machine (or vice versa) without anything more than an internet connection and making sure Dropbox is running on both machines.

The files are also stored on the Dropbox servers, so even if you don't elect to share with a friend, you've got an off-site backup just by using the tool.

Caveat: pick a friend you can trust to use Dropbox with for peer-to-peer sharing. They can see your Dropbox-shared files and you can see theirs. Files are encrypted on the Dropbox server, so no one but the accounts which you authorize can access them.

Dropbox is one example; perhaps the most popular. There are similar, competing services as well. Windows Live Mesh and SugarSync are two examples.


CrashPlan is backup software that, as one of its features, allows you to use a friend's remote computer as your backup storage location.

The beauty of this approach is that it's much more like backup software and can be configured and controlled more like backup software.

The free version allows only peer-to-peer backup with no storage provided by CrashPlan itself. It appears to be ad supported and does not offer "continuous update". Paid versions of the product offer these features and more.

Unlike the Dropbox approach, your data is encrypted before it leaves your machine, meaning that the friend who's been nice enough to allow you to backup to his machine elsewhere cannot see your data.

Disclaimer: I've not used CrashPlan, so this isn't really a recommendation. However, it is the only online backup service which I've found that has the very feature that you're asking for as part of its offering. Make sure to carefully evaluate this, or any product or service that you plan to use for backing up.

Online Services in General

If all that you're looking for is an off-site backup, you don't need the data to be stored on a friend's machine, and you can live with the assorted costs and/or limitations of the various services, then any of the general-purpose online backup services may well be worth looking into. Names like Carbonite, Mozy, Jungle Disk and others are examples.

Roll Your Own

For completeness, I'll throw this out as well.

Particularly because it's what I did.

While my wife had her business, my off-site solution consisted of two approaches:

  • I used a Hamachi VPN to connect the two machines over the internet, and then simply had batch files or scripts that copied files back and forth as appropriate. This backed up the most critical data nightly.

  • Each location had an external hard drive on to which more extensive, nightly local backups were placed. Periodically, we would physically swap the two drives as we traveled to and from the business.

The disk swap might not be seamlessly automatic, but it was quite practical.

Article C4802 - April 23, 2011 « »

Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

Not what you needed?

Michael Horowitz
April 24, 2011 11:25 AM

The security of Dropbox hosted files is apparently poor, employees of the company are able to decrypt your files. The other Leo (Laporte) suggested which competes with Dropbox but claims to be unable to decrypt your files on their servers. He hadn't actually used it however.

The Security Now podcast from April 20, 2011 described a security flaw in the Dropbox software. Apparently, copying a single file is all that's needed for a bad guy to impersonate you with Dropbox. Even if you change your Dropbox password, the bad guy with that critical file is still you, as far as Dropbox is concerned.

As for the common offsite backup providers, there is a hidden gotcha with some of them. I blogged about this here

Why your backups may disappear

In brief, they do replication rather than backup. Thus, if you accidentally delete a file on your computer, many providers will delete the backup of that file.

There is also another option: you can roll your own VPN. Windows XP Professional and some versions of Windows 7 (not sure which) are able to act as a VPN server. Probably Vista can do it too, not sure. Also not sure about Macs.

The upside is that by acting as your own VPN server, no extra software needs to be installed and thus no trust needs to be placed in any third party. And, its free forever. The downside is that its a bit techie to set up.

Finally, yet another option: sibling NAS boxes. Some (many?) Network Attached Storage devices are able to replicate the data they hold to another NAS box. They do incremental backups using rsync. Thus, its best to fully mirror the two boxes initially. Offsite replication can even be scheduled for off-hours. I haven't tried this yet, but would love to some day. Its a bit pricey however.

Mark Draa
April 26, 2011 10:27 AM

While online backup using these methods sounds good in theory, there is one overriding disadvantage that is rarely mentioned: ISP Data Caps. If your service provider limits your data transfer to, say 250GB per month (cough...Comcast...cough), and your normal usage accounts for say, 100GB per month, then your new online backup system would be limited to a transfer of 150GB per month. It sounds like a lot, but it's not. Given the potentially draconian penalties for exceeding the data cap, online backups are rarely practical.

Steve Clark
April 26, 2011 3:13 PM

For those, like me, with over 200 GB of data to backup, Crash plan offers (for a reasonable fee) a "seeded backup" service. They send you a hardrive, you backup to it, then return to them, they upload it to your online backup, all encrypted. Then your system can start maintaining that backup with just files that change or are added. Gets you immediate backup protection and saves all that data upload time. They will also overnight a drive back to you if you need to restore your system and don't want to wait for all that download time. They have the most options for data backup I have found. I have mine set to backup to a local eSATA drive and online to CrashPlan. I have used it to recover data after a hard drive crash. There is no option to do a full system backup or image backup. The user interface is a bit too simplified and not exactly well documented - that's my only complaint. Their tech support is pretty quick and helpful. I now subscribe to their family plan, backup as many as 10 computers, no data limit, no data transfer rate throttling either. And back to the article, it does support backing up to any other computer, whether its your own or a friend's. After many many years looking for the "right" backup solution, this is the best so far. I am a realist though and I would be surprised if Crashplan doesn't let me down somehow in the future, but so far so good!

Mark J
April 28, 2011 11:43 AM is a very good piece of software to connect computers over the Internet. It is expensive ($500) for professional use but it is totally free for non commercial use. Of course, you have to trust each other to give each other access to each other's computers.

Robin Clay
May 1, 2011 11:48 AM

Mark Draa wrote, April 26, 2011 10:27 AM :-

While online backup using these methods sounds good in theory, there is one overriding disadvantage that is rarely mentioned: ISP Data Caps.

In the "Good Old Days" before the Internet became so universal, I used "Fido", and also I used what might be called "Fido technology" to transfer files "direct" (i.e. without any InterNet/ISP etc.) to another computer via dial-up modem. I once (circa 1994) did this from a computer in Turkey to another in the UK.

Perhaps this might still be a viable method ?

Can one "dial-up" using the Internet telephone system ? If so, how ?

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