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What’s the Difference Between “Image” and “Clone”?

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I always seem to become confused when the discussion turns to image and cloneI thought I understand the basic difference, but … maybe not?

Image and clone are two very confusing backup terms.

One reason is a deep, dark, dirty little secret of the industry: we don’t all agree on what these two terms mean. Quite literally, one person’s clone is another person’s image, and vice versa.

It gets confusing, and if you’re hearing different things from different people, that’s why.

I’ll provide what I believe are the most accurate and common definitions. Hopefully, that means you’re more likely to hear people agree than disagree with what I’m saying.

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Clone

A clone is a bit-for-bit identical copy of a drive1.

To understand what that means, we need to review what’s typically on your computer’s hard disk drive. Content falls into three broad categories.

  • Overhead: boot information, partition information, the contents of recovery partitions, and so on.
  • Data: all of the files and folders on the hard disk, plus the information that allows the operating system to locate and manage them.
  • Free space: currently unused areas of the disk.

Another important thing to know is that data isn’t kept together on a hard drive. Particularly as you use it over time, data gets spread out over the disk, and when you delete a file, the area it occupied is marked as available (or free, or empty). The net result is that over time, portions (or “fragments”) of files are spread out over the entire hard disk, with free space between.

A clone is an exact duplicate of the original. Not only is all the overhead and data copied, but the content on the disk marked as free space is also copied. The exact layout and organization of all the data and free space is preserved.

Creating a Clone

The most common application of cloning is to make an identical copy of a physical hard drive and put it on a different physical hard drive. An application of this might be to have two drives in one machine. In fact, some people use this as a backup strategy; they have two identical drives in their machine, and periodically clone the drive they use to the backup drive. Essentially, they take a snapshot of their working drive. If they ever need to restore or replace the primary drive, they simply switch the cables so the backup drive becomes their working drive.

It is possible to clone a disk to a file. That file can then be used to restore that disk to its bit-for-bit identical state. A file containing a clone will generally be proportional in size to the original hard disk size (not accounting for any possible compression used to create the file).

Image

An image is a copy of all the information on a drive.

Like a clone, an image copies all of the overhead and data stored on a drive. Unlike a clone, an image does not copy free space, and it makes no attempt to preserve the physical layout. This doesn’t affect what you see in terms of where and how files appear as you use a drive; it only affects the physical location of the files on the disk media.

Create Image

An image is typically made to a file, rather than to another drive, so it’s often called an image file. A complete image of a hard drive still includes boot and partition information. In fact, when you fire up a tool like Macrium Reflect, one of the first things it does is display all the partitions on the hard drive. There are several of them, and if you say, “Back up all the partitions required for reinstalling Windows”, it selects several of them for you. That’s the partition information that gets stored in the resulting image file.

But this time, data and only data gets placed into the image. It includes all of the boot, partition, and overhead information, with your files and folders, and compiles it all into an image file. Since it doesn’t contain any of the drive marked as free space, an image is typically much smaller than the actual size of the drive you’re backing up; it’s proportional to how much disk space has actually been used.

A full-image backup has two main differences from a clone:

  • Free space is ignored.
  • The layout of the files on the disk is ignored.

Typically, an imaging program copies one file at a time. It looks for a file on C:, copies it to the image file, and moves on to the next file. That process removes any fragmentation present on the original drive. The net result is that the back-up file represents a completely defragmented image. In other words, all of the files are sitting next to each other, perfectly contiguous. When you restore an image file to an empty hard drive, all the files come back perfectly defragmented (in fact, that is one way to defragment a drive completely: back it up to an image and immediately restore it).

Image and clone: which do you want?

Now that we understand the difference, which one do you want to use?

My position is that for backing up your computer, you want an image. There’s no real added value from taking the extra time, space, and resources to create a clone. An image file ends up being smaller and significantly faster to create — and to restore, when the time comes.

When in doubt, choose image.

What Those Words MeanThis article is taken from What Those Words Mean, an overview of several of the most common and confusing terms used relating to backing up.

What Those Words Mean is based on a series of videos (also included) and is available in The Ask Leo! Store.

Podcast audio

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Footnotes & references

1: Or partition. The terms apply there as well, but I’ll keep the focus on entire drives here.

37 comments on “What’s the Difference Between “Image” and “Clone”?”

  1. Just to reinforce numerous articles written by Leo, I have found Macrium Reflect to be one of the very best – and free – imaging software programs available. I have taken and restored numerous images using MR. Top notch and rock-solid reliability. The fact that a free version is available is quite remarkable.

    I know there are other free imaging programs available. But MR has been so dependable for me, I see no reason to consider changing.

    Reply
    • I agree with you on the robustness of Macrium Reflect, but there is a good reason why some may prefer EaseUS Todo. The free version of Todo allows you do make incremental backups which is a very useful feature. If you don’t want incremental backups, or differential backups are good enough for your purposes, then I’d recommend Reflect. It all depends on your specific needs.

      Reply
      • I have used both of the mentioned programmes and find a flaw in both going from a large drive to a smaller drive fails every time. You may ask why would you want to do that ? well one reason is moving to an SSD drive there are other reasons, but the point is it does happen. The only program I have found that does this successfully every time is HD Clone 4.3 there is a free and a Pro version. and it really is the swiss army knife of clone/image software

        Reply
    • I have tried to use MR various times. After making an image I have it verified. When I need to restore, it never worked. Last time when I needed to revert from 10 to 7, because many of my programs did not work on 10, I had to reinstall 7 from scratch.

      Reply
  2. Have two Samsung SSD 120Gb 850 EVO……clone for b/u (I often ‘over-tweak W10). Using a 3.0 USB 7 x 15 SATA cord I can clone one to the other in <5min. BTW, I DO NOT USE MY DOCUMENTS in W10……use 1Tb 3.0 USB external hdd for that purpose.

    Reply
  3. Hi Leo, I have just finished reading the 2nd edition of your Macrium Reflect book. It is excellent.
    I have one question. Can I use 2 Seagate USB external hard drives on my desktop.

    Windows 10 does not support Windows Media Center. I had a full image backup of Windows 7
    on 9 DVD’s. Now the burner does not work. I had a G: for backup; but Microsoft wrote an F
    partition. I would like to dedicate a drive (external) to backups only. Is my thinking okay?

    Reply
    • There should be no problem attaching 2 external drives to your computer. I sometimes have up to 5 attached. A drive dedicated for backups is OK, but there’s no reason not to use the drive for other files as long as you have the space and back up that data too.

      Reply
  4. Either method is better than nothing, but I’ll never understand why imaging is “better”. I have two matched drives and update the cloned drive once a week. I can enter BIOS, change the sequence and boot to the second drive. I do this 3-4 times a year to ensure it worked. It has never failed. I ask imaging folks how often they boot to the backup to ensure it worked. Most have never even done that, or unsure how to do it.

    Many have a USB bootable drive that enables the image to be restored. I ask how many have tested the USB drive to ensure it actually boots, and a large number have never tried it. On many computers, one cannot boot to an ext drive without first enabling that feature but that can only be done inside Windows. The days of entering BIOS with an F key to change the boot sequence are long gone unless that feature was previously configured while in Windows.

    Many have ext image backups but never test them.

    Reply
    • You make a viable argument for cloned drives rather than an image backup.
      There are, however, a couple of advantages of an image backup, principally space and time savings, and also the fact that a restored image will give you a nearly 100% defragmented drive.

      Reply
  5. am i correct or INcorrect . . .???

    all of this time, i’ve generally made a point to stay away from “imaging” software, thinking that it – ENcodes – the data, meaning that you need to use their software to DEcode, which in an emergency may not be available

    please – what’s the situation?

    thanx!

    Reply
    • Imaging does produce file of a format only the program creating it can read, however, that’s what the rescue discs (usually CDs or bootable flash drives) are for. You can boot from that rescue media into an OS with a built-in version of the program you need to restore the image to a drive.

      Reply
  6. I’ve been using Macrium Reflect, with which I make images and clone my main drive to an extra internal drive. In a pinch, I’ve found it much easier to simply switch to my cloned drive, and I’m immediately off and running again! I update my cloned drive as I do my work, so it’s always up to date, and once a month re-clone in order to get all my Windows updates on the cloned drive. I also do a complete Macrium image every 2 weeks to cover my bases.

    Reply
  7. I have not done an image backup in a very long time. At that time I was using CDs for the image backup. After waiting over a half hour and not even a fraction of the backup done, I gave up. I had no idea of how much time or CDs the full image would take. I could only guess it would take just as long to restore if needed. I’m sure the method has been improved through the years. My clones take about 30 min. on a 1 T backup HDD. when completed, I use the backup HDD right away. I do this every month between 3 rotating HDD. This way I always have 2 backups.

    Reply
    • In the long run an external HDD would also turn out to be much cheaper. Backing up a 100 GB system would take about 20 DVDs. Assuming that costs $6.00, 8 backups would buy you a $50 – 2TB HDD.

      Reply
  8. Let’s say I make an “image” of my hard drive and have recently made a “rescue” disk. Soon after, my hard drives completely fails – for whatever reason. Would I be able to purchase a new hard drive – of the same size as the failed one; replace the failed drive with the new one; start the computer with the “rescue” disk and restore this “image” to the hard drive; remove the “rescue” disk from the computer; restart the computer and be back to a running computer at the state that existed at the time of the “image”?

    Reply
  9. Thank you, Leo. This is a very puzzling question I have been asking myself for years, and never found the answer to. (Years of using the paid version of Macrium Reflect, and reading their manuals and forum, I may add…) Thanks also to the commenters who explained how they use cloning to be sure their backup is working. That was certainly illuminating.

    By the way, making sure your system disk backup will work if you need it is one of the most irritating (and overlooked) problems… You once wrote an article on the subject, and if I remember correctly, your conclusion was that there was almost no way to simulate fully a restore operation for verification purposes… Hence the point of cloning. Please correct me if I’m wrong.

    Reply
    • It’s not “the point” of cloning at all. Cloning serves certain purposes, but imaging it perfectly valid for 90% of most users. You can’t “test” a clone without taking it live, which, depending on your technique, may have the same issues as testing an image.

      Reply
      • After I make a clone of my HDD, I don’t take it live to test it. I actually use it for the entire month. I then make a clone on a third HDD and do the same. After the month, I use the first HDD to make a clone. At all times I have two HDD I can use if my operational drive fails. Also I do not need to use the same size or type of drive, even SSD drives.

        Reply
  10. Speaking of defragmentation, here is an interesting discussion on the Macrium Reflect forum (by people who image for backup, of course, as opposed to cloning) :

    http://support.macrium.com/topic.asp?TOPIC_ID=5174

    The gist of the matter being : if you want to keep your images quick and small, you should defragment just after the last incremental and before the next full image, and not in-between a series of incrementals.

    One of the reasons of preferring Macrium over other imaging software, for me, has been their forum (forum of version 5, that is ; I have just upgraded to version 6, and haven’t tested the new forum). Some regulars that populated it were obviously very knowledgeable users, being in charge of IT in professional settings, and sharing their very useful experience.

    That’s also one of the reasons for preferring the paid-for version over the free one, by the way. You can’t ask questions on the forum without a licence number. And Macrium is now rather pricey : the cheapest version is 63 € for a single PC.

    Reply
  11. I have found this article and discussion very interesting, but it seems that the failure of a system in all scenarios discussed,
    assume a mechanical failure or breakdown.
    If a Clone or Image are used as the basis of restoring a system and the system failed due to a software or virus type issue, don’t you run the risk of starting the restored system with the issues that caused the failure ?
    Would it not be beneficial to do a complete re-install of your operating system and software, then copy the files that you have backed up to the new system.
    For this reason I back up my documents, pictures, music, address book , emails and any other files that I have created. This takes up less space in back-up too.
    Am I being too simplistic. Is my method ok for a single home computer?

    Reply
    • As long as you restored to a backup taken before the malware or software failure occurred, it wouldn’t carry the virus or software issue with it. Of course, you’d have to be sure the computer was issue free when the backup was take. Your method would work, and it is the most sure method, but it would mean a lot more work on your part.

      Reply
  12. I`m using the free version of xxclone for many years and I find it very useful. If I am not mistaken it is doing fragmentation at the same at the same time of cloning.

    Reply
  13. mine is easy I don’t keep any thing of importance on the computer I have never trusted any backup so don’t keep anything there that has to be backed up

    Reply
    • A backup image can still really help in the case of malware. You may not have a lot of data, but you do still have programs… even your operating system is a program. So with an image you can restore to a known version of your machine if anything goes wrong.

      Reply
    • I hope you’re right. In my experience people who make this “nothing important” assumption often find out that they were wrong, that something important was lost – forever – when their computer died. What that might be is anyone’s guess – there’s no way to predict it – but I’d bet money that there’s something on your computer you’d be sorry to miss.

      And, as Connie mentioned, there’s malware.

      Reply
  14. Very interesting and possibly the software outfits (Acronis) are part of the confusion because I’m quite sure I cloned Win 7 from a 1TB HD to a 500 GIG. I’m certainly no expert but I have picked up info. over the dozen years since I got my first computer when I was 69. Back in early summer with my i52500k and 8 ram on a Seagate 1TB and the threat of Win 10 and my more knowledgeable son-in-law, my font of extra HDs, we were trying to move Win 7 to a 500 GIG. S-i-l had always used imaging and supplied Acronis Rescue V8 but we had problems so having access to the 2015 version we tried it and still had problems when I suggested cloning which I should have known would be impossible. Anyway I proceeded and it was trying but claimed the image too large so I went back into Explorer deleting everything possible and hit a mine full of Sys. Restore files. In the end it was satisfied and wrote to the formatted 500 GIG HD after which I told Win 10 to take over and did a custom transition. There were some initial boot problems on 7 which the chkdisc utility fixed up.

    Today everything is ticking along perfectly. I type this in Firefox on PCLinuxOS (which works like a Swiss Watch) which I use 90% +. My wife uses Win 7 offline for all her graphics work in Photoshop and I occasionally go into creaky Win 10 (which works like a sundial on an overcast day).

    Reply
  15. Leo,
    Seems to me that cloning may have an advantage over imaging since you only copy to a new HDD and then swap it whereas imaging requires to copy and then the extra (risky?) step to restore it.

    Reply
  16. Hello! I’m not sure if you’re still answering questions here, but I have some doubts on the topic, and your feedback would be much apreciated.

    I really liked your article, and your definition on cloning and imaging made more sense than most explanations I read around the internet.
    However, it seems like most people consider that the difference between cloning and imaging is that the first makes a copy to a drive, ready to boot, and the other one creates the compressed file. And even explanations made from backup software companies seem to have this definition in mind.
    So, how can we know exactly what kind of copy we are getting of our drive (with or without free spaces and fragmentations and stuff) if we can’t rely on them calling it ‘imaging’ or ‘cloning’?

    For example, how can I make a clone of my drive to a compressed file? I know of software that creates images…but I want the Exact copy. Maybe they do it, but call it Imaging. How would I know??
    I also never heard of any software making Images directly to a disk… How can we do that?

    Reply
  17. Lets say i lost all the partition on my disk and now its just blank no systeme nothing! and i want make a copy of the whole data to another external disk this data should make me later restore my old files like videos and photos what should i do? image?

    Reply
    • You can try one of the data recovery tools available first. A tool like Recuva may help, for example, but there are others.

      You may not be able to image, since that tends to assume a working file system. You MAY be able to clone.

      Reply

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