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B.2.3. Using Free Space from an Active Partition

This is the most common situation. It is also, unfortunately, the hardest to handle. The main problem is that, even if you have enough free space, it is presently allocated to a partition that is already in use. If you purchased a computer with pre-installed software, the hard disk most likely has one massive partition holding the operating system and data.
Aside from adding a new hard drive to your system, you have two choices:
Destructive Repartitioning
In this case, the single large partition is deleted and several smaller ones are created instead. Any data held in the original partition is destroyed. This means that making a complete backup is necessary. It is highly recommended to make two backups, use verification (if available in your backup software), and try to read data from the backup before deleting the partition.

Warning

If an operating system was installed on that partition, it must be reinstalled if you want to use that system as well. Be aware that some computers sold with pre-installed operating systems may not include the installation media to reinstall the original operating system. You should check whether this applies to your system is before you destroy your original partition and its operating system installation.
After creating a smaller partition for your existing operating system, you can reinstall software, restore your data, and start the installation. Figure B.10, “Disk Drive Being Destructively Repartitioned” shows this being done.
Disk Drive Being Destructively Repartitioned
Image of a disk drive being destructively repartitioned, where 1 represents before and 2 represents after.
Figure B.10. Disk Drive Being Destructively Repartitioned

In the above example, 1 represents before and 2 represents after.

Warning

Any data previously present in the original partition is lost.
Non-Destructive Repartitioning
With non-destructive repartitioning you execute a program that makes a big partition smaller without losing any of the files stored in that partition. This method is usually reliable, but can be very time-consuming on large drives.
While the process of non-destructive repartitioning is rather straightforward, there are three steps involved:
  1. Compress and backup existing data
  2. Resize the existing partition
  3. Create new partition(s)
Each step is described further in more detail.

B.2.3.1. Compress Existing Data

As the following figure shows, the first step is to compress the data in your existing partition. The reason for doing this is to rearrange the data such that it maximizes the available free space at the "end" of the partition.
Disk Drive Being Compressed
Image of a disk drive being compressed, where 1 represents before and 2 represents after.
Figure B.11. Disk Drive Being Compressed

In the above example, 1 represents before and 2 represents after.
This step is crucial. Without it, the location of the data could prevent the partition from being resized to the extent desired. Note also that, for one reason or another, some data cannot be moved. If this is the case (and it severely restricts the size of your new partition(s)), you may be forced to destructively repartition your disk.