GPT boot with ZFS RAIDZ "ZFS: i/o error - all block copies unavailable"

[Krzysztof Dajka]

I still can't boot. I don't know whether I missed it in first time,
but I'm getting
>ZFS: i/o error - all block copies unavailable
x6 before seeing boot manager. I tried booting with verbose option,
but there was only laconic

>Trying to mount root from zfs:zroot
>ROOT MOUNT ERROR

When I execute lsdev I'm getting
....
disk devices:
       disk0: BIOS drive C:
            disk0p1: FreeBSD boot
            disk0p2: FreeBSD swap
            disk0p3: FreeBSD ZFS
       disk1: BIOS drive D:
            disk1p1: FreeBSD boot
            disk1p2: FreeBSD swap
            disk1p3: FreeBSD ZFS
       disk2: BIOS drive E:
            disk2p1: FreeBSD boot
            disk2p2: FreeBSD swap
            disk2p3: FreeBSD ZFS
pxe devices:
zfs devices:
       zfs0:      zroot

I can also do `ls` and I can browse whole zroot, and everything seems
to be there. At least for the boot loader.