I am building a video storage server at home, but I have ran into a problem in my plans. My original plan was to use TrueNAS Scale with ZFS and start with a mirrored vdev of two 18TB drives. I then wanted to expand it one 18TB drive at a time into a Z1 vdev of about 5 drives. However I found out from online research that it is not possible to just convert mirror vdev to a Z1 or even expand a Z1 vdev. Does a software raid solution exist where it is possible to start with just two drives, add other drives later and still keep the n+1 topology? This is the minimum I need, however the possibility to add an extra parrity drive would also be amazing. Let’s say once I get to 5 drives (4+1) I could add an extra parrity drive to get 4+2. Is this somehow possible? If so what solution should I look into?
As it was said, you may try unRAID which would handle even the different size drives.
As alternative, it looks like mdadm should fit your requirements. You can use smth like openmediavault for that.