Hard drives fail fast (in comparison) and the new solid state drives are no better and some worse than the spinning platter.
Backup drives, that are not in use (unpowered), almost never fail. I keep two backups (drives are cheap), in addition to main music drive, just in case of something bad happening during updates (second backup in different location in case of fire, theft, etc). The chance of failure of two unpowered drives in storage is pretty much zero. As for the SSD - the main problem is limited number of writes to each sector - completely unimportant in this application. Again - unpowered drives don’t likely fail.