I wasn't sure that it was this way.
My install suppose a use of SSD for Nextcloud web-server with apps, user's accounts, services and database. Users data is located on ZFS raid.
/mnt/raid/nc:/var/www/html/data - this is user's default folder in Nextcloud.
/mnt/pool/photo:/mnt/pool/photo:ro - this is folder for "external storage". I mounted it with the same folders paths to avoid mistakes.
I have now enough fast reaction from Nextcloud in this configuration rather than in my previous setup with all Nextcloud & DB folders located on HDDs.