Use all space in raid-z on disks of different capacities?

Question

ZFS

Greetings!
Zfs felt quite a bit in 2016 in freeNAS. As far as I understand, raid in zfs is assembled from partitions, without being tied to physical media. There are 2 disks of 3TB, and 2 disks of 500GB. I would like to assemble a raid-z1 from 4 disks using "kids" of 500GB each, and later upgrade all disks to 3TB. Is it possible to make a raid-z on 4 partitions of 500GB on each disk, having received 1.5 TB of effective space in raid-z1 and the remaining 2.5 TB on each disk, either temporarily use it without raid, or in a mirror?

Answer 1

I would like to assemble a raid-z1 from 4 disks using "kids" of 500GB each, and later upgrade all disks to 3TB.

Do it. This is a pretty standard option. Subsequently, you will make zpool set autoexpand=on <pool>and through you zpool replace <pool> <device> [new-device]will replace the disks. After the last drive is replaced, the pool will automatically expand to the new capacity.
Nobody can stop you from shooting yourself in the foot. By doing so, you should be aware that you are creating an increased load on these two disks with all the consequences.

Answer 2

It is recommended to give the entire disk to ZFS so that the data is written block to block and there is no performance degradation.