Question about the choice of file type

Hello,
I come to you hoping to find the solution most suited to my needs.

I have an HP DL380e server with 2xE5-2450L and 32 GB of ECC ram.I was thinking of going on a RAID5 mount in ext4.
Following the advice of @cabrio_leo on other topics, I thought I was moving towards the ZFS format (32GB of ram that seems to be well suited), I was seduced by the possibilities and security that offers this format.

Currently testing the possibilities of different formats and following the creation of a RAIDZ-1, I realized that it was not possible to enlarge a RAIDZ-1que by adding to the initial pool another RAIDZ-1 (so 3 disks minimum then again 3 discs etc ...).

I want a solution that is at least as reliable as RAID5 and with the ability to add volumes without having to add them by 3 disks like ZFS.

Is there currently a format compatible with OMV in the same genre as ZFS, but without the constraint of adding the disks by 3 as in the case of RAIDZ1?

thank you in advance

Quote from cabrio_leo

You can expand the pool not only by another RAIDZ-1 (in your case), but with any kind of ZFS volume.

SnapRaid

My ultimate goal is to have 2 pools of 6-7 disks (in RAIDZ1 ideally). If I add a disk in another format than RAIDZ1, as a basic disk or a mirror, yes, it will be present, but not in RAIDZ1, is that it?
If my request above is correct, you must at least add at least 3 disks for RAIDZ1.

Regarding SnapRaid I will look at this thank you.

Edit: Following the reading on the forum topic about snapraid and a very good comparative table, I think indeed that snapraid is the most flexible for the use I want to make. I was going to explore in this way. thanks again @cabrio_leo