[ZFS install/boot fails; no such pool and/or Could not find the root block device]

I ran into this problem when upgrading ZFS from 0.6.5 to 0.7.5.

I resolved it with brute force.

When you run genkernel initramfs, it generates this warning:

* WARNING... WARNING... WARNING...
* Additional kernel cmdline arguments that *may* be required to boot properly...
* add "dozfs" for ZFS volume management support
* add either "real_root=ZFS" (bootfs autodetection) or "real_root=ZFS=<dataset>" to boot from a ZFS dataset

I heeded this warning and in /etc/default/grub I changed it from:

GRUB_CMDLINE_LINUX="dozfs real_root=ZFS=rpool/ROOT/funtoo"

to:

GRUB_CMDLINE_LINUX="dozfs real_root=ZFS"

Also worth noting is that I only ran into this problem on my server, which runs ZFS with mirrored VDEVs.

I had initially created the server pool with the following command:

root@ubuntu:~# zpool create -f -o ashift=12 -o cachefile=/tmp/zpool.cache -O normalization=formD -O atime=off -m none -R /mnt/funtoo rpool mirror /dev/disk/by-id/foo /dev/disk/by-id/foo mirror /dev/disk/by-id/foo /dev/disk/by-id/foo

My desktop computer, which runs a single disk pool as described in the ZFS install guide, was able to update ZFS successfully, without having to change it to bootfs autodetection.

I am not sure if this is a regression with GRUB or ZFS, but these were my observations. Try it out and see if it resolves the problem for you.