Demystifying the Backup

Category: Backup

The apparently simple task of backing up one’s data is not so simple when you start reading advertisements and reviews of backup software. “It does full, partial, and incremental backups; mirrors and clones disk drives…” Let's take these terms and explain them all in plain English...

Making a Backup: Options and Terminology

What do all these geeky buzzwords mean, and what kind of backups should you being doing? If you're just as confused about backups as the guys on the Seinfeld show, you'll find this article helpful. Let’s start by explaining some common types of backups, without the techie jargon.

A “full backup” is also called a “system image” in computer parlance. It is a copy of an entire hard drive’s contents, from the boot record to the last file you created or changed by clicking Save or Send. System settings, the Windows registry, hidden files such as the page file and hibernation file, everything on your hard drive is saved as a single file on your backup media (usually an external hard drive or network-attached storage device). If you've ever created a ZIP file, it's similar in concept -- lots of files combined into one large file.

backup terminology

Sometimes compression or encryption techniques are used to save space or secure the image file. The advantage of an image file over just copying a bunch of files to a backup device is the convenience of having just one file, especially if you want to store the backup in more than one location.

Full backups are somtimes made when a system is “just right,” with everything installed and set the way its owner wants it. A computer can be restored to that ideal state from a full backup copy. Another benefit of a full backup is that it’s easily restored; just read the whole file, unravel the digital “packing material” from each system file, and write it to the hard drive.

If you need to recover from a disk disaster quickly, a full image backup is good to have. Depending on your needs, and how often you add, delete or update files, you might decide to make an image backup on a weekly, monthly or other timeframes.

But full backups can take a long time, and a lot of storage space, so it's generally not a good idea to do them on a daily basis. Only a small percentage of files change from one day to the next. So why should they be copied and stored in a backup file again and again? That's where incrementals come in handy.

Incremental and Differential Backups

Incremental backups make backup copies only of files that have been modified or created since the last backup session. First a full backup is made; it serves as a reference point. Thereafter, only the files that have been created or changed (since the last full or incremental backup) are backed up. To restore a crashed system, you need to start by restoring the full backup copy. Then every incremental backup made since that full backup was created must be applied in the order they were made.

A differential backup is similar, in that it saves data that has changed (or been created) since the last full backup. Each differential backup contains ALL of the differences between the last full backup and the current state of the hard drive. It has the advantage of requiring only two sets of data – the full backup and the latest differential backup – to restore a system to its most recent state. The downside is that more data needs to be backed up in each differential since the last full backup.

Here's a simplified illustation to make that a bit clearer. Let's say you make a full image backup every Sunday morning, then every day, you create one new document. Daily incremental backups would each contain ONLY that one new file. But the daily differential backups would contain one, then two, then three, and finally six files by the end of the week. The nuances of incremental and differential really aren't so important. Years ago, when hard drives were much slower, storage space was more expensive, and processing power was limited, it made more of a difference. The more important thing is that you actually DO make an image backup on a regular schedule, and supplement it as files are created or updated.

More Backup Buzzwords

A bit of confusion exists over the terms “image,” “clone,” and “mirror.” All three are full backups of a hard drive, but they're each distinct. I've already defined image, which is basically the entire contents of a hard drive rolled up into one large file. Cloning means making an exact file-for-file copy of one hard drive on another drive. Mirroring is an ongoing process; as data is added, deleted or changed on the original disk, it is mirrored to the backup disk.

Synchronization, or “sync,” is a two-way street. In a traditional backup, data from the source drive is backed up to a destination drive. In syncing, data is continuously copied from drive to drive so each drive contains exactly the same files and versions of those files as the other. Syncing is most commonly used on a folder basis, for example, when you want all of your music or documents to be available on multiple devices.

Versioning is a feature that some backup programs offer, which allows you to keep multiple backups of frequently updated files. If you have a document or spreadsheet that's updated on a daily basis, and you want to see what it looked like yesterday, last week or last month, versioning is just the ticket. It can also save your bacon if you make accidental changes to a file and then save it, wiping out the original. Think of versioning as the "undo button" you can use *after* you save and close a file.

Whatever sort of backup you do, you will end up with multiple backup copies taken at different points in time. How long you want to keep backup copies is up to you, unless you’re in a business whose “records retention” policies are regulated by law.

I've been intentionally vague here about specific tools you can use for backups, imaging, cloning, and other ways to protect yourself from data disasters. That's because my article Free Backup Software Options goes into more specifics about some excellent, free software you can download to get started with your own backup plan.

Are you using backup software to protect your most important data? Post a comment or question below...

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Most recent comments on "Demystifying the Backup"

Posted by:

10 Feb 2014

I've been using the free version of Macrium Reflect for a couple of years. I've actually done an image restore several times so I know it works.It's compatible on all versions of Windows(although on Windows 8 you'll have to disable Secure Boot in order to boot from the CD). I highly recommend it for any backup situation.

Posted by:

10 Feb 2014

Bob, Windows 8 seems to have done away with scheduled backups. Did I miss something, or should I use third party software for backing up my files? Thanks.

Posted by:

10 Feb 2014

Thanks for this very timely post Bob. I've been putting off for a long time doing a backup, even though I knew I should, I'd usually just get confused with jargon, and decide to wait for some mythical new insight to help this old dinosaur to get it done. I'm still using XP pro, and don't really want to change, but know I'll have to pretty soon as right now,my "D" drive isn't even recognized (not listed with my other drives), and whenever I have to do a restart, I have to press F1, as it says windows can't find a primary drive. Why? It's beyond me to what happened, and none of my slightly more talented computer friends can figure it out either. I'd hate to take it into a shop, and pay them to tell me that it would cost nearly what I could get a new machine for. On a very limited SS check, that's a big deal. Wish I'd learned more about backups before I lost my "D" drive, cause I don't think this big external is going to be any help to do this. Getting your newsletter has taught me many things, except how to fix my "get around to it".

Posted by:

10 Feb 2014

Is there some backup software that does not compress the files (esp. when it's in a proprietary way)? I like to peruse my backup files from time to time to ensure everything I need saved is saved...and only those things.

Posted by:

bob price
10 Feb 2014

Very good explanation of the terms, thanks. It can be confusing. But methinks any article on backups should include any complications when restoring.

The article states "Whatever sort of backup you do, you will end up with multiple backup copies taken at different points in time."

This is only true with images. A clone backup is a total file by file copy of the drive, and the good ones are bootable. Simply change boot sequence and boot to the backup.

Can you boot to an image backup or does it need a created CD/DVD?

Posted by:

10 Feb 2014

I use Macrium Reflect because of Bob's recommendation. It is uber-easy to use, and free! I make a new image every month or so, keep the latest three, and delete the oldest image after the new one is complete. I have not had to use it to restore an image yet (thank goodness!), but I know it's there if I need it.

Posted by:

10 Feb 2014

Many thanks, Bob for a very detailed explanation. The fun usually starts when a file restore is attempted and you are given a lot of confusing options. If Windows fails all your backups won't help if you can't access the computer so I looked for a bu program such as Acronis that provides its own boot capabilities.

Posted by:

BallyIrish Bob
10 Feb 2014

Thank you Bob, you make it so easy to understand. I purchased your book on Backups quite some time ago from which I gained a good understanding of backups, which was always something I dreaded, as I just could not grasp all the nuances prior to being educated by you. I gave up trying to use FBackup, Easeus Todo, Macrium Reflect, COMODO Backup etc, as I found them just too complicated.

So I stick with AOMEI Backupper on both my Windows and XP Home. I find it very easy to use and it makes a disk image in a jiffy. There are some instructive You Tube videos on how to use AOMEI.

The native Windows 7 Backup and Restore facility is a bit of a failure in my experience, although easy to understand. However I kept getting an error message, even when trying to backup - even to a newly formatted external HDD: whereas AOMEI just gets the job done now!

Posted by:

10 Feb 2014

Yeah, I know very few people use this, but Windows Home Server makes backup stupid simple. Both image and file backups, and versioning for all connected client computers. At $50 it's very reasonable, though you have to supply a spare computer to run it on. And you get all the benefits a (home) server gives you: shared files, media server, remote access, etc.
Caution: Microsoft in it's infinite wisdom has decided to cancel WHS - apparently it didn't make the $millions they wanted. Get it while you can.

Posted by:

11 Feb 2014

Great, informative article. Question. If this was covered I missed it. Suppose I do an image backup of my desktop hard drive. Then I purchase a new PC with upgraded operating moving from Win 7 to Win 8.1. Then what. Is my image useless? In this case would I not need a copy of all files other than the system files? This sort of thing is getting beyond my pay grade. If you have time. Thanks in advance for an answer.

EDITOR'S NOTE: Macrium and others allow you to "mount" an image file, and copy out just certain files or folders.

Posted by:

11 Feb 2014

I've used Macrium Reflect for several years and it's my favorite of all I've used. I keep 2 copies of my System Drive (just in case) with 4 differential backups per week.

As for the question by Josil above...With Macrium you can double click on your backup and it will go to a virtual drive and allow you check it's contents. I use the paid version and that capability may not be on the free version. Not sure about that.

Posted by:

11 Feb 2014

While all Bob's articles are both interesting & informative, this one was particularly so.
I use "Easy Backup' perhaps not the best but at least it is easy !

Posted by:

Stanley J.Solomon
12 Feb 2014

For better or worse and for good or faulty reasons, some to many sophisticated (at least partially?) home computer user have a hard disk that has been divided into more than one partition. Given this structure, the second paragraph of Making a Backup: Options and Terminology strike me as incomplete and/or incorrect.
For a disk with a single partition a "full backup" will contain a boot record as well as the user data that had been written to it. Because this backup has a boot record, it can, as I understand it, be written to a new, blank hard drive as well as to the disk from which it originated.
If I make a "full backup" of, say, the third partition on a hard disk, this backup will not include a boot record. Consequently, while it can be written back to the original disk, it can not be written to a new, blank hard drive until after that drive has been partitioned.
Am I correct that this second kind of "full backup" would not contain a boot record?

EDITOR'S NOTE: Maybe I don't fully understand the question, but you can't write ANYTHING to a new, blank hard drive until it has been formatted and has at least one partition. There's no requirement to write a boot record to a single new partition on a shiny new hard drive, either. A partition can contain only data if desired, and no boot record or operating system files.

Yes, one can make a backup of a single partition, and if that partition has no boot record, it obviously can't be used to boot a PC. But nothing prevents one from making an image file that contains ALL partitions on a drive.

Posted by:

Steve in Raleigh
20 Dec 2014

So Bob, do you like the discontinued MS Home Server, or FreeNAS, for setting up a home server using old desktop hardware? And do you strongly recommend going with a new SSD, or is using a medium aged HDD OK? Looking at this as a central home server and backup, along with SugarSync (which I've been using a while). Two laptops run Windows 7 (one is 32 and the newer is 64), and with NT running on lightly used HP desktop.

Posted by:

Rob Henderson
02 Aug 2017

Thanks for the clear concise explanation of the "differences" between differential and incremental backups. Macrium Reflect 6 allows only full and differential backups on their free program. Incremental has to be paid for. With 3 TB backup drives free is just fine.

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