Originally Posted by saltynay
Mechanical hdds need to be defragged as they have magnetic distrotion over time as the data is stored using very powerful magnetic fields.
Defragging has nothing to do with the magnetization of the grains. Defragging makes logical files/fragments contiguous in order to minimize wasted seeks and consequent delays in file read/write. File fragmentation is specific to the file system and has nothing to do with the hardware since the latter is abstracted from the former. An SSD will suffer file fragmentation just like a magnetic HDD, although the effects of this fragmentation will be different in each case.
Data storage on magnetic drives is done by magnetizing the 'grains' of the magnetic thin film (on the platter) in a specific direction; the boundaries in the transition region determine the bit. Excellent explanation is available here:
Storage Technology / Patterned Magnetic Media
The magnetic 'distortion' will occur only if the magnetic domain size is small enough that ambient thermal energy causes randomization of the magnetic moments (superparamagnetism). Such fine grained films are not used in magnetic storage media precisely for this reason. Instead, patterned magnetic media will be used to overcome the superparamagnetic effect. If you heat up your drive to too high a temperature, then you may lose your data
...but under normal operating conditions, magnetic 'distortion' is not an issue unless there is material degradation/damage.
BTW, SSDs may not suffer from file fragmentation for reads, but random write performance is supposed to be badly hit by free space fragmentation.
Diskeeper has an add-on called HyperFast that optimizes random write performance by minimizing free space fragmentation. It's part of the Diskeeper 2009 package...I noticed it on my DK2009 Pro install but since I don't have an SSD, I couldn't check what it does.
Also: The Diskeeper Blog: HyperFast is also here!
recommends not defragging an SSD as a magnetic HDD, but doing the free space consolidation instead.