HELIOS4 (32bit) NAS - Best Option

I'm going to guess that is highly unlikely considering Helios dropped support in '21.

Definitely a cool device, and I almost bought a Helios64, but this is part of the danger of buying niche appliances like this that don't have serious money backing them... they run the risk of collapse and you have a cool desktop ornament.

You can try just installing 32bit Bookworm on it and see what happens... Of course then the issue becomes it's 32bit. which in my opinion is almost useless save for a SMB server

Sometimes it's cool figuring out something to do with old hardware... and sometimes, you need to understand there's a reason there's electronic recycling centers out there.

If you'd consider an upgrade; install OMV7 on Armbian's Bookwork -> CLI version.
Install -> OMV7.

If you're looking to stretch the Helios4's useful life, this might be the best option. You'd get updates for awhile.

But, as KM0201 said, the CPU (and image) is 32bit.

I've never attempted a ZFS install on a 32bit device, or an ARM device, so I don't know it's a possibility in OMV.

Since OMV-extras is installed on your Helios4, as part of the scripted install, you could look for the ZFS plugin (openmediavault-zfs) under System, Plugins. If it's not there, and you attempt create a pool on the CLI, OMV won't integrate the pool, filesystems, etc., into the GUI. That means you won't be able to create network shares in the GUI.
__________________________________________________________________________

If ZFS is not possible, you still have options. (I'm going to assume that you want to use all 4 of the drive bays.)

Traditional (mdadm) RAID:
Since the Helios4 uses SATA drive connections, you might be able to configure RAID in the GUI (Under Storage, Software RAID). In your case, RAID5 and two RAID1 pairs are possible. With traditional RAID5, you might consider using an UPS.
(I'm not a fan of traditional RAID but many use it.)

Rsycn:
You could do two each Drive-to-Drive Rsync'ed pairs which are the equivalent of RAID1. (I'd argue that an Rsycn mirror is better than tradtional RAID1 because you'd have real backup.) -> Rsync.

-> SnapRAID + -> MergerFS:
This pair of packages would give you the equivalent of RAID5, with a number of additional benefits such as data integrity, file and folder recovery, and others. But, there's some reading to do to understand them. The plugin doc's cover the basics of each plugin in an overview format. They can be used together or separately. They're not interdependent.

BTRFS:
(I don't know if BTRFS is available to ARM and/or 32bit.) Similar to ZFS, BTRFS snapshots are supported in OMV along with other features. The only caveat would be for BTRFS RAID5; just as it is with traditional RAID5, you should consider using an UPS. (That's not a bad idea in any case.)

JBOD:
There's nothing preventing from you from formatting each disk and simply assigning individual network shares to each drive. Other than ease of management, there's no requirement to pool disks together.

zfs does install on arm and even 32 bit. But you need to use zfs-dkms and it is MUCH better to install the kernel headers and get zfs-dkms installed before the plugin is installed. But, I wouldn't use zfs on those boards.

Please note, as ryecoaaron has said, this comes with risks and it's not supported. (The build warning should have been clear.)

With that said;
Run the following on the CLI as root

zfs set aclmode=passthrough hdpool

zfs set aclinherit=passthrough hdpool

zfs set acltype=posixacl hdpool

zfs set xattr=sa hdpool

zfs set compression=lz4 hdpool

If you decide to use ACL's at some point, the above will be helpful.
(The last is optional. Your call. )

Don't forget to create child filesystems on the parent pool. The filesystem level is where you should create your shares. In my case, I've created a separate filesystem for each share. That let's me customize ZFS properties for each share and to take individual filesystem snapshots.

Along those lines, if you want to automate snapshots, give this -> doc a look. It also covers how to do selective restores.

You've already named the pool (hdpool)

In my case I set filesystems, at the root of the pool, to segregate data types. That allows for setting ZFS properties for each filesystem (if needed) but what I was most interested in was creating custom snapshot intervals for certain data types by filesystem. For instance, (even after they're deleted) I retain copies of personal documents for a year, before zfs-auto-snapshot purges them. That allows for plenty of time to discover an unintentional delete or to pull back a previous file version. On the other hand, after being deleted, video files are retained for 30 days before they're permanently purged.

Following is an example of how I segregate data types:



There's no right or wrong way, just personal preference.