Cannot speak to using a 18TB drive in a second gen single bay My Cloud; but while waiting for a Synology NAS a few years back, I did test out using shucked WD 12TB Easystore drives in a first gen single bay My Cloud. It worked fine once properly “unbricked” for the first gen. Moved the shucked Easystore 12TB’s to the Synology after playing around with them on the first gen single bay My Cloud for a few hours.
See my post at the following URL about using the 12TB’s on a first gen single bay My Cloud.
