A better solution (which could be used in addition to periodic erasure) would be to store the data encrypted, and hold the key in volatile memory. Reliably eras

A better solution (which could be used in addition to periodic erasure) would be to store the data encrypted, and hold the key in volatile memory. Reliably erasing data from hard disks (particularly if they're SSDs with their own controller) is a tricky business. There's little to stop someone just removing the disk from the machine and getting hold of whatever was stored on it at the time, or improperly disposing of it if the machine breaks.