镜像数据库 "%1" 包含的事务日志数据不足，无法保留主体数据库的日志备份链。如果没有从主体数据库进行日志备份或者没有在镜像数据库上还原日志备份，则可能会出现这种情况。

The mirror database, "%1", has insufficient transaction log data to preserve the log backup chain of the principal database. This may happen if a log backup from the principal database has not been taken or has not been restored on the mirror database.