ffmpeg Does using SSD improve render times when disk usage 100%?
Try using one disk for source material and a separate disk for the rendered video output. 

There are lots of different SSD disks - cheap MLC ones, and more expensive but faster SLC ones. 

If using RAID, there are several types. RAID5 and RAID1 probably won't be faster. RAID0 (striped array) is intended to be faster than a single disk. 

What interface are you using? If you are using it as a removable drive, have you changed it to allow write-behind caching? (This allows the computer to move on while the drive is still writing the buffer to disk)