I like and use iDefrag 2.0.0. But I encountered one near-fatal problem with a feature the second time I used it. Too lazy to take the extra steps to reboot to a different drive, I used the little white tab on "Go" to allow me to defrag Metadata from the boot drive. There is of course a reboot to give iD2 exclusive access to the drive. I started the program, and went to bed. A few hours later I found the program had stalled, no evidence of a power interruption, and a disk that not only wouldn't reboot, it couldn't be found by Disk Utility or Disk Warrior or Startup on SysPref using my backup drive. Lucky for me, I had just backed up to that second drive, and was able to recreate the whole volume as it had been. As I indicated I had already used this feature once successfully with this healthy drive. And it cured me of laziness in restarting from a different drive to begin with.