I would note however that the RPis can be spectacularly bad when they start thrashing, irrespective of whether they're running from an SD-Card, SSD or rotating media.
Thrashing hardly happens when:
- Using a power supply > 2.5A combined with:
- Using a premium brand SD card (class 10)
BTW I boot some RPi's from a Sandisk 64GB USB drive and that is rock solid.
A good power supply is a *must*, otherwise you take the risk of trashing yourself.
What also helps is connect a powered USB extension hub when you run rotating media: hard disks can be power hungry.