ZFS: i/o error all block copies unavailable Invalid format

[KOT MATPOCKuH]

Hello all!

On 24 nov I updated sources via csup to RELENG_9 (9.0-PRERELEASE).
After make installboot I successfully booted to single user.
But after make installworld system was fail to boot with message:
ZFS: i/o error all block copies unavailable
Invalid format

status command shows status of all polls properly.
root filesystem is not compressed.

# zfsboottest /dev/gpt/rootdisk /dev/gpt/rootmirr
  pool: sunway
config:

        NAME STATE
        sunway ONLINE
          mirror ONLINE
            gpt/rootdisk ONLINE
            gpt/rootmirr ONLINE

Restore of old /boot/zfsloader was solved issue.
Before I successfully updated 4 another systems with same sources
level without any problems.

My sys/boot/zfs/zfsimpl.c's version: 1.17.2.2 2011/11/19 10:49:03

Where may a root cause of problem? And how I can debug this problem?

-- 
MATPOCKuH