Hi Lugs

I was amazed how easy it is to set up Nextcloud on a Raspberry Pi using the NextcloudPi image (once I'd bought a bigger SD card). It works even on a first generation Pi but some things are slow, login via the web, moving around directories and apps. I've just bought a new Pi4 which I assume will be a lot faster but I already have about 50GB of files on an external HD attached to the original Pi. It took a long time to put them there and I'd rather like to avoid doing it again.

Does anyone have experience of attaching an external drive with existing data to a new Pi?

During installation of NextcloudPi there's an option to use external (USB) storage but it assumes a new disk and formats it. No good in my case. If I decline that and just set up on SD card how hard is it to mount an HD later without losing the data already on it?