SvenHz

Here is an update. TL;DR: happy to report that zfs 2.0.2 seems to work fine on Armbian Hirsute.
 
I am planning a reinstall of our "family production NAS" with the aim to do as little hacking/customization as possible to get ZFS to work.
 
First I tried both the current (Mar 2021) Buster and Focal images but failed at the 'apt install zfs-dkms' step due to "exec format error" and basically failing to produce a working kernel module for ZFS. I suspect this is caused by the older binutils on both images.
 
So then I downloaded the Ubuntu Hirsute unstable image with kernel 5.10.23 of 13 Mar 2021. Supplied binutils is 2.36 I believe.

After the clean install, these are the steps I took:
 
# apt update
# apt upgrade
Use armbian-config to install kernel headers (turns out to be 5.10.17)
Use armbian-config to downgrade kernel 5.10.23 to 5.10.17 to match old headers...
# apt install zfs-dkms
 

apt install zfsutils-linux
 
 
After this and a reboot, I successfully imported an existing (zfs 0.7.x) pool.

So far so good. I will wait until we are stable with Hirsute.
 

Here is an update. TL;DR: happy to report that zfs 2.0.2 seems to work fine on Armbian Hirsute.
 
I am planning a reinstall of our "family production NAS" with the aim to do as little hacking/customization as possible to get ZFS to work.
 
First I tried both the current (Mar 2021) Buster and Focal images but failed at the 'apt install zfs-dkms' step due to "exec format error" and basically failing to produce a working kernel module for ZFS. I suspect this is caused by the older binutils on both images.
 
So then I downloaded the Ubuntu Hirsute unstable image with kernel 5.10.23 of 13 Mar 2021. Supplied binutils is 2.36 I believe.

After the clean install, these are the steps I took:
 
# apt update
# apt upgrade
Use armbian-config to install kernel headers (turns out to be 5.10.17)
Use armbian-config to downgrade kernel 5.10.23 to 5.10.17 to match old headers...
# apt install zfs-dkms
 

apt install zfsutils-linux
 
 
After this and a reboot, I successfully imported an existing (zfs 0.7.x) pool.

So far so good. I will wait until we are stable with Hirsute.
 

This has been fixed via a patch to mvebu-current (LK5.10) so should be available via nightly or with the next armbian release : https://github.com/armbian/build/blob/master/patch/kernel/mvebu-current/0001-Revert-block-simplify-set_init_blocksize-to-regain-l.patch

It is fixed in LK 5.11 in mainline, but unsure if Armbian will get LK5.11 on mvebu or if we wait until the next LTS kernel version.

Done

There are problems with 32bit ZFS support and there is nothing more we can do. 
https://github.com/armbian/build/pull/2547 
https://github.com/openzfs/zfs/issues/9392
Broken od Debian, buildable on Ubuntu based Armbian. At least on latest (LTS) kernel 5.10.y

Upgrade to 5.10.y on 32bit target doesn't work automatically ...
 
 after reboot you need to run 
dpkg-reconfigure zfs-dkms and select that you agree with 32b troubles but at the end, it works. I could load my pool without issues.