A relevant performance consideration that most people don't pay attention to is how
full their hard disk is. The amount of free space on a hard disk affects the performance
of the drive, for most of the same reasons that partitioning
affects it:
- The more data on the volume, the more the data is spread out over the disk, reducing positioning performance;
- A disk that is more full forces new files to the inner tracks of the disk where transfer performance is reduced; and
- Drives that are full both take longer to defragment and tend to be more fragmented in
the first place.
The "Peter Principle" of hard disks is that the amount of junk put on a hard
disk expands to fill the available space, regardless of the size of the hard disk. Imagine
what PC users 10 years ago would have thought about people with 6 GB hard disks needing an
upgrade because their "disk is too full!" I had the personal experience the
other day of surprisingly discovering that a 15 GB hard disk volume I had just installed
was down to 2 GB free! Most people don't clean out their disks until they have to. 
The bottom line though is clear: the more "stuff" you put on that humongous
hard disk you just bought, the more you will slow it down. Don't fill your drive with
clutter just because you have the space. Regularly go through your hard disk to get rid of
files you don't need; if you think you will need them "at some point" then
archive them to a tape, CD-R disk or other removable medium.
Another impact of this is that you cannot reliably compare performance benchmarks even on the same disk in the same
system if you change the amount of data on the drive between runs. All drives will tend to
show a reduction in performance as you fill them up, so benchmarking should always be done
on empty drives to eliminate this variable.
Next: Fragmentation
