boot failure after upgrade to HEAD from svn: zfs i/o error - all block copies unavailable invalid format

[乔楚]

*Today, after **upgrade to HEAD from svn, My FreeBSD can't boot.*

*Error message:*

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


*If boot from **FreeBSD-11.0-CURRENT-amd64-20131205-r258961-bootonly.iso
or FreeBSD-11.0-CURRENT-amd64-20131205-r258961-disc1.iso, boot loader
will stop at *mountfrom:


*My FreeBSD version is -current.*

*Before upgrade, svn version is r25906.*

*After upgrade , svn version maybe r**259156.*

*ZFS is root fs.*


*How to fix it?*