SIsirn·Nov 12, 2022
The problem is, ZFS support on GRUB2 hasn't been great, partly due to CDDL/GPL licensing incompatibility requiring lots of ZFS internals to be re-implemented in GRUB. This resulted in issues such as grub-probe unable to detect ZFS pools due to unsupported ZFS features[1] (including native ZFS encryption, which is a deal-breaker for many)
ZBM took another approach. It provides a small initramfs image that are built on the host machine via standard method such as dracut or mkinitcpio. This image provides an interface for decrypting/mounting ZFS filesystems using the very same ZFS kernel module and tools installed on the host. After the filesystem is mounted, it then kexec'd into the host kernel.
This also means ZBM doesn't completely replaced GRUB2 or syslinux. Instead, it rely on those intermediate bootloader (including EFI bootloader such
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as rEFId/gummiboot) to load ZBM itself. (Though ZBM itself only has built-in hooks for syslinux and gummiboot).
Being an initramfs give an extra benefit of providing interesting mechanism during boot e.g. providing a SSH server for entering an encryption key on a headless server[2], ability to discover, managing/booting from ZFS snapshots, etc.
(No affiliate; just a very happy user.)
[1]: https://savannah.gnu.org/bugs/?58555
[2]: https://github.com/zbm-dev/zfsbootmenu/wiki/Remote-Access-to...