Nextcloudpi SD card fills up.

[default_user8]

Ok, i'm just going to admit to being lazy and ask, can you point me somewhere that will show me how to boot from the SD and run from a harddrive on the rock64.  When i was  using raspberrry pi's it was set up to boot from a usb drive, but i'm not that familiar with my rock64's yet.

P.S.  I forgot to add i figured out what was filling up my SD card.  I mirror my main drive to another drive with a cron job.  My cron job was writing to my SD card instead of my backup hard drive.

I followed some direction in this forum a long time ago, but the short version is this:
* write an image to a sdcard and hdd
* using gparted rename the main hdd partition to be rootfs
* then in the fstab on both I changed the root partition to be rootfs
* edited the /etc/default/extlinux and /boot/extlinux/extlinux.conf to be root=LABEL=rootfs

Haha, i said i was being lazy, guess i was being stupid too, I forgot all about uboot.  Got my nextcloud up and running on an 80gb harddrive i attached via a usb 3.0 adapter.  Thanks for the help,  there is virtually no traffic in this forum compared to the raspberry pi community it's nice to get a reply.