Q: How Fragmented Should My Hard Drive Be. Before I Should Defrag It ?
A: I would say you should be defrag-ing your computer at or before 5% fragmentation rate. Any more and it could take several hours to defrag. (Will depends on your hard drive and system states. It will also depend on what disk defrag program you are using. Some are faster then others.)
Your not gonna harm your computer hard drive. If you want to defrag your hard drive before it reaches 5%. I feel 5% is easy to remember and it also means your system is not to far gone. By about 8% your system may become affected by the fragmentation of your main hard drive. And slow down your computer start-up and shut down process may increase by quite a bit. So watch out for that symptom.
Now if we are talking a periodically used extremal drive (Unless it is a direct back-up for your C:\ drive). You can wait way past 5% to defrag your hard drive. For me I add and subtract files all the time from my many external drives. So there really is no point as that hard drive is pretty much always under 3% fragmentation rate.
Till The Next Q+A,