Defragmenting?

It rearranges files' location in the partition to place them in consecutive clusters, so that the system has faster access to them. The free space of the partition becomes then one or more large blocks. It is good to defragment a disk before software installation.

To be sure that you don't loose your data, you have:
1. to take regular backups.
2. to use a UPS, because a failure in electric supply could damage filesystem records.

Disk fragmentation is one of the microsoft systems problems. Even with the windows defragmenter we can't have all the free space in one block at the end of the partition. If the disk occupied space is more than 50%, there are always more problems (especially in server systems).