Extending RAID-Z1 with smaller disk

[struthio]

hi,

I am planing to rebuild my NAS and I would like about approach I want to take before I start so I will not end up in dead-end.
I have current nas with two drives 10TB and 12TB that are just regular drives (without ZFS). I am currently planning to upgrade my NAS with 2x12TB drives and went with ZFS RAID-Z1 for 1 disk failure protection.

Current drives have data in it, and I was planning to do migration in a way:

1. From 2 new 12TB drives create new RAID-Z1
2. Copy data from existing NAS 12TB drive to new RAID-Z1
3. 12TB which I just cleared add as another drive to RAID-Z1 (now 3 12TB drives will be in RAID-Z1)
4. Move data from 10TB drive to RAID-Z1
5. Extend RAID-Z1 with cleared 10TB drive

Yes I know that adding smaller drive will reduce usable space on 12TB to 10TB but that is not an issue.

My question is: Can I extend existing RAID-Z1 with smaller 10TB drive OR added drive have to be equal size or larger than drives in pool ?

[struthio]

I will answer myself :) Is is not possible. If You try to add smaller sized disk, ZFS will return a message saying disk is too small.

[IvanVolosyuk]

If you are willing to waste 2TB per disk you can create 10TB partition on each 12TB disk and create raidz from those. There is a temptation to create another raidz vdev for those 2TB chunk and put it into the same pool, but it will cause unbalanced allocations and issues with performance. You can have those 3x2TB in a separate pool with cold data though.