Using partitions with disk image backups

In my posting last week, The best defense against software problems: disk imaging, I tried to make a case for disk image backups. They are the Rodney Dangerfield of software, they get no respect. I've read hundreds of articles and blogs that offered poor advice to a whole host of problems, simply because the author was not familiar with disk imaging. I can't stress this enough:

Disk image backups can fix every software problem.

Infected with malware? Restore a recent disk image backup.

Windows won't boot? Restore a recent disk image backup.

Your computer no longer knows about your printer? Restore a recent disk image backup.

Frequent Blue Screen of Death? Restore a recent image backup.

Computer running much slower than it used to? Restore it to an image when it was faster.

Disk imaging doesn't just help with software. Want a bigger, faster hard drive? Make an image backup, replace the hard drive, restore the image backup. Hard drive failing? Failed? Buy a new one, then restore the latest image backup.

A computer without an image backup is like a car without a spare tire in the trunk or an airplane flying without a co-pilot. If your computer is important to you, you don't want to be one glitch away from a computing disaster.


But, there's a problem: data files. The above scenarious are great for the operating system and your applications, but not for your data files. What you really want is to restore the operating system and applications but not down-level all your data files at the same time.

That's where partitioning comes in.

Hard disk partitions can isolate the executable stuff from your data. The end result is a C disk containing Windows and applications and an X disk (any unused letter will do) containing data files.

This does, however, mean getting in the habit of looking for all files on X instead of C and saving all files to X instead of C.

In addition to letting you backup and restore just the operating system and applications, you also benefit in that the OS partition will be much smaller without your data files. Thus image backups run faster and take up less space.


A hard drive can have up to four partitions and chances are that the hard drives you deal with have more than one.

Not all partitions are visible, many PCs ship with hidden partitions. If your operating system thinks the hard drive is signficantly smaller than the size advertised for the computer, then the difference is probably due to a hidden partition.

Windows XP users can see their hard disk partitions by right clicking on My Computer, selecting Manage, then Disk Management. 

Perhaps the most common use for a hidden partition is storing a factory fresh copy of the operating system. I've also seen partitions used for diagnostic purposes; where pressing a particular key during startup invokes diagnostic programs in the hidden partition.

Partitions are either primary or extended. Extended partitions were an enhancement, created to break through the limit of four partitions. There can be only one extended partition, but it can host multiple "logical" partitions.

Windows boots from a primary partition known as the "active" partition. Only one partition can be flagged as active.

A data-only partition can be either a primary or logical/extended partition. My preference, built up over years of playing with partitions, is to use a logical partition.

So, how is a C disk split into two partitions? 


First, you should verify that the file system is problem-free. In Windows XP, open My Computer, get the properties of the C disk, go to the Tools tab, then click on the Check Now button. Turn on both checkboxes, we want to fix any problems that are found and also scan for bad sectors. Then re-start Windows. After Windows boots, check the Application Event log, looking for a recent entry with a Source of Winlogon. That's where you'll find a summary of the disk analysis.

Next, run a full defrag.

If you use any hard disk diagnostic programs, this would be a good time to run them. Steve Gibson's SpinRite is king of the hill, but pricey. A free alternative is HD Tune. Each hard drive manufacturer also offers free diagnostic software. SpinRite's big advantage is that it can fix certain types of hard disk errors. 

Finally, make an image backup of the C disk partition. Modifying partitions can be dangerous.  


The first step is to shrink the C disk partition.

There is no one right size, it depends on the version of Windows and your installed applications. The good news is that you don't need to chose a perfect size, it can always be changed later.

On a new computer, shrink the C disk down to the size of the used space plus 10 - 20GB to allow for new applications. On a computer that's been used for a while, you can get a good estimate of how big to make the C disk partition by moving data files off to an external drive. Then, as with a new machine, re-size the C disk partition to the used space while still leaving room for installing new applications. I have found 10 to 20GB to be a generous allotment for new applications, but your mileage may vary.

On a well used computer, the simplest approach is to shrink the C disk down to the currently used space plus a few gigabytes for good luck. When you eventually move data files into their own partition, this will free up space in the C disk partition that can be used for installing new applications in the future.  

After shrinking the C disk partition, you are left with unallocated space on the hard disk. Not to be too nerdy, but free space is allocated to a partition, but not being used. Unallocated space doesn't belong to any partition.

The next step is to create an extended partition that completely fills the unallocated space.

Finally, create a logical partition that completely fills the extended partition.

When creating a logical partition, you get to chose the file system, Windows users should opt for NTFS. You also get to name it, so pick something self-explanatory such as "mydata" or "dataonly". Being a Star Trek fan, I have, at times, used "MrData". 

Next time, thoughts on partitioning software.


Copyright © 2009 IDG Communications, Inc.

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