icehot said:
as defragmentation must not be done too frequently for better hard disk life.
Not true.
If a drive is fragmented badly, then the drive life may be reduced because the actuator arm has to work needlessly to place/pick up non-contiguous pieces of the file, when writing/reading the file. Defragmentation arranges the file parts contiguously, and therefore reduces drive workload.
If you defrag regularly, as your usage patterns dictate, then successive defrags will take up much less time and fragmentation will be under control.
There is nothing like defragging too frequently since, if the drive is not fragmented, then the defragmenting software will simply have no work to do, and terminate within a few seconds or minutes.