This web page from Crucial will help with your questions. Briefly do not defrag an SSD. Do not regard an SSD as an HDD, they are 2 different beasts. Also have a look at this web page at digital citizen which describes the TRIM command.
My new laptop has an SSD and I wondered how Dell configures them for defragmentation because so many people say they should not be defragged. Can anyone advise me of this pls?
Defragmenting an SSD