Defrag a SSD will not improve performance, actually it could decrease performance due to the fact that a lot of file copies would be made, filling the SSD with more garbage to SSD garbage collector:
Defragmenting an SSD is a terrible idea, for several reasons:
The key benefit to SSDs is that they have virtually no seek time.
Reading adjacent blocks of data is no faster than reading blocks that
are spread out over the drive. Fragmentation does not affect SSD drive
speed.
As I discussed in my SSD Remaining Drive Life article, SSD drives
physically wear out as you write to them. Defragmentation software
moves around all the files on your drive. Thus, defragmenting an SSD
reduces its life span without giving you any benefits.
SSD drives deal with the limited lifespan of their memory cells by
using wear-leveling algorithms. These algorithms take advantage of the
fact that fragmentation does not affect the drive’s speed. They
purposely fragment the drive so that its cells wear out evenly, even
if you’re constantly overwriting a small set of files (e.g. database
fiels) and never overwriting other files (e.g. operating system
files).
Modern SSDs even lie to the operating system. If the operating system
tells the drive to save a file in blocks 728, 729, and 730, the drive
may decide to write it to blocks 17, 7829, and 78918 instead, if it
determines that those blocks haven’t been worn out as much yet. The
drive keeps a lookup table of all its blocks, so that when the OS
wants to read blocks 728 through 730, the drive reads blocks 17, 7829,
and 78918. With such drives, defragmentation software can’t possibly
work. The software will think and tell the user that file X was nicely
defragmented and stored in blocks 728, 729, and 730, while it actually
has no idea where the data is stored physically on the drive.
Conclusion: don’t waste your time and your SSD’s life expectancy by
defragmenting it. The automatic defragmentation in Windows 7 skips
SSDs automatically. In Vista, you can disable it via the Performance
Information and Tools item in the Control Panel. I do strongly
recommend you upgrade to Windows 7 if you have an SSD, so you get TRIM
support.