Should Database Servers Be Defragmented? I've never been clear on this point - should Windows servers running SQL Server ever be defragmented with a tool such as Smart Defrag or Windows' Disk Defragmenter?
Provided you recon 100% that physical disk fragmentation is significantly affecting sql server performance and you can afford downtime, go for disk defrag.

I have never had to defrag a windows disk hosting sql server databases. You should choose a sensible autogrowth value for your databases and have Instant file initialization enabled.