Solar storms are no joke

> Even when the storm passed and the systems came back online, data in magnetic storage (including all hard drives and SSDs) would have been irrecoverably damaged.

SSDs? Would even actual magnetic storage like hard drives really be damaged? If I understand correctly the electromagnetic 'pulse' would come very slowly, cause huge spikes on long wires like electric distribution networks, but I don't see how it would wipe disks unless it's just by way of forcing lots of uncontrolled power from the electrical outlets through the computer. Would that really happen? Also, mobile devices not attached to the grid would then still work, also PCs not currently connected.