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22 Nov 2016

Techie Tuesday: Image or Clone?

Disk Cloning vs Disk Imaging: What’s the Difference?

The reason for the confusion about the difference between disk imaging and disk cloning is that both achieve the same end result. They replicate the contents of a hard drive.

Data, files, software, the master boot record, allocation table, and everything else needed to boot and run your operating system, both a disk image and a disk clone can comprehensively capture everything that makes your machine run. This means they are both powerful techniques that can help you to quickly recover your PC if your hard drive fails or becomes corrupt.

However, the subtle technical differences between a disk image and a disk clone are important. While you shouldn’t see one approach as being “better” than another, once you compare them, you’ll have a much better sense of the relative benefits and disadvantages of both. This means you’ll be able to make an informed decision about the right way to go about copying a hard drive for your needs.

In this post we’ll take a closer look at what a disk image is, what a disk clone is, and how to go about evaluating the right approach.

What is a Disk Image?

A disk image stores all of the information required to completely restore specific disks (or their individual partitions) exactly as they were when the image was taken. It essentially compresses all the data on your hard drive into something that can be more easily stored (and, if needed, later recovered).

If you want to, you can even store several compressed disk images onto one large external storage device (provided it has enough storage, of course). This which gives you multiple options when it comes to restoring an image.

While this is a reliable way to backup your PC — after all, a disk image is a pretty comprehensive copy of your hard drive, repeating the process can be slow. Moreover, images can fill your backup media very quickly.

Fortunately, there is a way round this, Once you have created an initial full image, you can then create differential and incremental images. These are both quicker to execute than full images and create much smaller image files.

What is a Differential Image?

A differential image stores the changes that have been made to the imaged file system since the last full image. Subsequent differentials can be taken, but only one differential and the full are required in order to fully restore the system. This is quicker than creating a full image. However the longer the time between the full image and the differential image, the larger the differential image file is. That means it’s going to take longer to create it.

What About Incremental Images?

Incremental images differ from differential images in that they only store file system changes since the last image, either full, differential or incremental. The resulting backup set therefore consists of a full image and a number of incremental images which must all be present in order to restore the system correctly.

Ultimately, this demonstrates one of the key advantages of disk imaging — its flexibility. However, as you can see, this flexibility comes at a cost — time. Disk imaging can be a slow process; this might not ordinarily matter but sometimes you might just want to move your hard drive quickly with as little fuss as possible. This is where disk cloning comes in.

What is Disk Cloning?

A disk clone is an an exact copy of an entire hard drive, or specific partitions on a hard drive. Unlike a disk image, it is uncompressed, which means it can immediately be moved to a different drive. Once you do this, everything on the target disk will be overwritten and you’ll be left with two identical drives.

When is Disk Cloning Useful?

Disk cloning offers a key advantage over disk imaging: it’s much faster. For example, if you are upgrading to a larger hard drive or moving from a large magnetic hard disk to a smaller and faster SSD, cloning your hard drive will provide you with a really quick way to get up and running in no time.

When you clone a hard drive, you can boot from the target disk on the same system with the state of your computer at the time you undertook the clone. But Windows cannot boot from a USB connected drive; this is a restriction imposed by Windows. You can clone to a hard drive installed in your computer or to a hard drive installed in a USB hard-drive Caddy. If you clone your system disk to a USB connected external drive then, to boot your clone the physical disk must be removed from the USB caddy and attached to your Motherboard SATA port.

How Do Disk Imaging and Disk Cloning Compare?

Disk imaging and disk cloning are both incredibly powerful techniques that can help you replicate and recover data. However, despite their similarities, they are both well suited to specific use cases — disk imaging gives you the flexibility that you need to reliably and consistently backup your PC, while disk cloning gives you the speed and convenience to replicate and move your existing hard drive incredibly.

Ultimately, then, deciding which approach to use comes down to what you’re trying to do. So, while you might want to use cloning to move your existing HDD to an SSD, once you’ve done this, you should probably use imaging to successfully backup your systems in a way that’s safe and storage-friendly.

You can read more about disk cloning and imaging here: Macrium KnowledgeBase: Backup, imaging and cloning

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