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Backing up to a second physical internal drive can be a surprisingly reasonable tool in your backup arsenal as long as you understand its limitations.

I have two very large internal hard drives. One has my OS on it that I use as my C: drive and for daily use and the other is one that I use for pictures and so on. Is it OK to backup the system (on C:) to the other extra internal HD? Or should I be using an external HD for that?

Yes, but...

Backing up to an internal drive isn't really all that different from backing up to an external one.

Each has its pros and cons - as do some of the other backup options that you might consider.

I'll walk you through the most common options.

Backing up to the same drive

Before I discuss your scenario, let's look at the scenario that makes the most knowledgeable techies cringe: backing up to the same drive.

For example, let's say you back up your documents folder to another documents folder elsewhere on the same drive - maybe the contents of C:\Users\You\Documents gets backed up to C:\Backups.

Pros (what this protects you from):

  • Accidentally erasing, modifying, corrupting or otherwise damaging your documents. You can simply restore them from the backup copy.

"... backing up to a second internal drive is a surprisingly reasonable choice ..."

Cons (what this does not protect you from):

  • Hardware failure. If your single hard-disk drive dies, you lose everything on it, including your backups.

  • System failure. When using this approach, it's difficult (if not impossible) to actually back up your entire system. If your Windows installation fails for any reason, this is not an approach that will allow you to simply revert to a backup copy.

  • Malware. If viruses or other forms of malware corrupt your system, your files or even entire drives - both the original and backup copy on the same drive - would be at risk.

  • Theft, fire, tornadoes, earthquakes, and the like.

Backing up to an external drive

This is a very commonly recommended approach. In fact, it's what I often tell people: "Get an external drive and some backup software and make sure that your system is getting backed up regularly".


  • You're protected from accidentally erasing, modifying, corrupting or otherwise damaging your documents. You can simply restore them from the backup copy.

  • You're protected from hardware failure. If your system hard-disk drive dies, you simply replace it and restore from the backup. (If the backup hard drive dies, you replace it and resume backing up.)

  • You're protected from most system failures. If you configure a complete system/image backup of your system drive to your external drive, then you can revert to a backup copy rather than having to reinstall Windows from scratch should your Windows installation fail for any reason.

  • You're protected against most malware. Recovering from a malware infestation would involve simply restoring from a full system backup taken prior to the infestation.


  • Some malware can infect all connected drives, so your backup drive (and possibly your backup system) could still be infected.

  • You're not protected against theft or disasters that would take out all of the computer-related equipment in your home.

All in all, it's a pretty reasonable list - that's a long list of pros without too many cons.

Backing up to an internal drive

Important: We're talking about backing up to a second physically distinct drive. Backing up to a different partition that resides on the same drive is not what I'm discussing, as it is exactly like backing up to the same drive, as mentioned above.

The only basic difference between backing up to a second internal drive versus an external drive is the connection and the location of the drive. Pretty much all of the pros and cons of the external scenario still apply.

There are a few subtle differences:

  • The internal drive will be faster. Thus, it's more likely to get used for day-to-day things as well as backups. How that day-to-day usage impacts the backups will vary; typically, the impact is disk space. In addition, some alternate means of backing up that data needs to be considered.

  • An external drive is typically more electrically isolated from system; this means that certain types of PC power supply or other electrical failures that might damage an internal drive might not damage an external drive.

  • An external drive is quickly and easily replaced, making it easy to upgrade or swap out as needed. Unfortunately, it also often makes the external drive easier to steal.

Short summary: Backing up to a second internal drive is a surprisingly reasonable choice and shares most of the same characteristics as backing up to an external drive. Some of the differences boil down to convenience.

Backing up to offline media

Offline media - typically CDs and DVDs, but this might also include flash media - have been a common form of backup for a while.

The single biggest "pro" to most of these backup destinations is that they are either write-once media and cannot be modified after the backup is complete or they're disconnected from the computer after the backup so that they're not impacted by any subsequent failures on that machine.

Of course, the "con" is that they're now relatively small compared to the amount of data that we typically want to backup. Backing up of anything large, particularly a complete system, so far exceeds the capacity of individual media that trying to do so becomes unwieldy.

Online backup

In many ways, online backups have the promise of being the holy grail of backups. They protect what's backed up from almost everything practically imaginable.

With one huge "con" - which is a fatal flaw, in my opinion.

Like backing up to individual media like CDs or DVDs, the amount of data that would need to be backed up for a full system backup is so huge as to make online backups totally impractical for full backups. A complete system backup would take days, if not weeks, to upload to an online solution.

Unless you can upload a terabyte in an hour (just over 2.4 Gbit/s, sustained), online backups are best used to backup important data but cannot be used to back up your system.


As you might imagine, backing up in any form is better than not backing up at all. Exactly how you should back up depends on your abilities and your needs.

One of the reasons that folks such as myself often recommend an external drive and backup software is because it's easy to set up and it gets you significant backup coverage from the most common disasters (hard drive failures and most malware).

And, if it's easy, then more people are likely to do it.

Backing up to a second internal drive could well be a worthwhile approach as long as you understand what is and is not being protected as a result.

Article C4833 - June 1, 2011 « »

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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?

Mark J
June 2, 2011 5:22 AM

I use BackBlaze online backup. (Carbonite might be as good or better but I'm traumatized by all of their hype.) I have an iso image of all of my installation disks in a folder which is included in that backup. I have on external drive with a Paragon disk image backup. I use another drive for backing up the My Documents folder which I set up to hold all of my data, since for some reason MS decided with Windows 7 to move a lot of stuff to the User Folder. I have a Dropbox folder to back up and synchronize my most important data. And to top off my paranoia, I have a GMail account which downloads a copy of all of the emails from all of my email accounts. If any body has any recommendations to add to that let me know and I might implement them.

June 7, 2011 8:45 AM

Salesman suggested external backup is better because lightning is less apt to destroy an external drive than an internal, because it would have to run into the computer to destroy an internal, but would also have to run out of the computer to destroy the external. Your thoughts?

Technically correct - internal drives are subject to whatever happens to the internal electonics and powersupply. However it's an edge case - meaning I don't see it as all that likely.

Tony M.
June 7, 2011 8:59 AM

I've been using Windows Home Server (WHS) for a few years, but I think I'd like to "graduate" to a NAS. I think a NAS might be safer and easier. I fear that trying to restore my WHS, if/when it fails, might be a little more "hairy" than just using a NAS. Any thoughts, anyone?

June 7, 2011 10:37 AM

I use both, internal and external. The external, a USB drive that gets connected ONLY when I backup. I don't need to backup that much so once every other week suits me.

June 7, 2011 10:51 AM

Another component of a good backup strategy is to take advantage of RAID1. Obviously I say component because you are still "backing up" (mirroring actually) to another internal drive.

Peter Mackin
June 7, 2011 2:36 PM

@Leonard: I disagree with salesman. The external drive (if it has an external power supply that is plugged into an outlet) is probably more likely to get fried by lightning since the power supply for this external drive is less likely to be able to withstand a voltage spike than the power supply in the PC. Of course, if everything is plugged into a good surge protector this is probably a moot point. Therefore, I guess I agree with Leo, it is an "edge" case.

Jim de Graff
June 7, 2011 2:51 PM

I use Acronis to back up to a separate internal drive. It's faster than backing up to an external USB drive. I keep the current backup on the internal drive and several generations on the external. Copying the internal backup to the external drive is faster than doing the backup to the external directly because only copying is done - not analysis and compression.

June 7, 2011 4:04 PM

About the lightning strike. If you get unlucky a major hit hitting close to the house will fry the surge protector. Read carefully fewer than 1 in 10 even say lightning resistant , way fewer say lightning protection and a close strike can & probably will fry those. Remember even a cell phone in your hand makes you a target. Old story I was backing up floppy to floppy and a strike going back fried data on both but did not damage the computer. If you get an early 100,000 amp hit close be thankful if you are still alive to worry about your data.

Serge Decoste
June 7, 2011 4:27 PM

If your house or apartment burn down, your HD or DVD backup is gone.
The only way, is to backup on a DVD and store it in your bank.

Rob Healey
June 7, 2011 6:27 PM

I had 3 separate internal drives and a month ago the power supply went up with a BANG. It killed all 3 drives (and the motherboard). Luckily it was my spare computer, no data was lost.

On my master PC I have two one Tera drives and was using the second one to backup the first- not any more!!! I am now using Acronis to backup to a Two Tera external hard drive.

The ideal situation would also be to backup to an external drive that was kept somewhere away from the house, which would be safe from Burglary or fire. I haven't worked out how to do that yet!!

Thanks Leo, keep these extremely useful articles coming.

June 8, 2011 12:45 AM

I have two internal hard drives, so as to be able to use one for backup. Each has two or more partitions: one for my data (except the stuff in Documents and Settings - yes, I'm still using XP) and one for the system. By using XXClone, I can backup C: to R: (a primary partition on the other hard drive) in about 12 minutes and boot to it any time I want to. I have even XXCloned to other partitions for particular reasons. Unfortunately, this method can't be used for Vista or Win7, which is one reason I'm sticking with XP.

Backup of data I do selectively, using either XXCopy or Robocopy.

All cheap, and fairly simple.

I've never needed to to worry about power problems, here in UK, so I only have a cheap surge limiter and a USB powered external hard drive.

Charles Miller
June 8, 2011 11:24 AM

Question, If I use a external. or internal drive for backups, does it backup everything, like operating system, If something happened to my main drive, would I be able to boot right off my back up drive, and not know any difference. I now copy important stuff to thumb drive, and into dropbox. Guess Im asking is it a perfect copy.

You can get drive imaging or cloning software that makes a perfect copy, yes. Most backup programs do not - they save all the information, but in a more compact form that must first be "restored" before you can use it.

September 28, 2012 11:56 PM

Another option if using a desktop is to fit a HD drawer to a spare bay which combines the internal/external drive cons by allowing quick & easy swapping of internal HDs.
Cheaper, faster & just as secure once removed.
An added advantage is the ability to immediately test a new system image by swapping the HD boot order in BIOS.

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