测试环境：    
原有存储是两个独立控制器+磁盘柜，目前是一个控制器+磁盘柜。开机启动时，先开启扩展柜，一分钟后开启控制器。发现系统起不来，经过多次尝试失败后，决定通过维护模式进入系统进行查看。（类似于Windows7的维护模式一样）

问题处理：    
开机boot启动项，按Ctrl+C命令中断正常启动，进入到boot menu菜单。    
Starting AUTOBOOT press Ctrl-C to abort...    
Loading X86_64/freebsd/p_w_picpath1/kernel:0x200000/10088648 0xb9f0c8/4301024 Entry at 0x80271e20    
Loading X86_64/freebsd/p_w_picpath1/platform.ko:0xfba000/1990365 0x11a0000/296352 0x11e85a0/273360    
Starting program at 0x80271e20    
NetApp Data ONTAP 8.3.1P2    
Copyright (C) 1992-2015 NetApp.    
All rights reserved.    
Checking boot device filesystem    
** /dev/da0s1    
** Phase 1 - Read and Compare FATs    
** Phase 2 - Check Cluster Chains    
** Phase 3 - Checking Directories    
** Phase 4 - Checking for Lost Files    
69 files, 1011584 free (31612 clusters)    
MARK FILE SYSTEM CLEAN? yes    
MARKING FILE SYSTEM CLEAN    
Retry #1 of 5: /sbin/fsck_msdosfs /dev/da0s1    
Retry #2 of 5: /sbin/fsck_msdosfs /dev/da0s1    
Repaired boot device filesystem    
*******************************    
*                             *    
* Press Ctrl-C for Boot Menu. *    
*                             *    
*******************************     
^CBoot Menu will be available.

WARNING:  The battery is unfit to retain data during a power  
          outage.  This is likely because the battery is    
          discharged but could be due to other temporary    
          conditions.    
          When the battery is ready, the boot process will    
          complete and services will be engaged.    
          To override this delay, press 'c' followed by 'Enter'    
c

CAUTION: Using this appliance without NVRAM  
         battery backup coupled with a power    
         failure condition CAN CAUSE DATA LOSS.    
Are you sure you want to continue (y or n)? y    
Proceeding without NVRAM battery backup.

Please choose one of the following:

(1) Normal Boot.        #正常启动    
(2) Boot without /etc/rc.   #启动存储时，不执行/etc/rc设置参数    
(3) Change password.      #如果忘记了超级用户密码，可以在此修改    
(4) Clean configuration and initialize all disks. #清除配置，初始化所有的磁盘    
(5) Maintenance mode boot.  #进入维护模式，当系统进不去的时候可以尝试用维护模式进入    
(6) Update flash from backup config. #从备份配置中升级flash    
(7) Install new software first.    #安装新的软件    
(8) Reboot node.         #重启节点    
Selection (1-8)? 5    
ixgbe: e1a: ** JUMBOMBUF DEBUG ** switching to large buffers(9k -> 3k): (sz = 5120)!    
ixgbe: e1b: ** JUMBOMBUF DEBUG ** switching to large buffers(9k -> 3k): (sz = 5120)!    
ixgbe: e2a: ** JUMBOMBUF DEBUG ** switching to large buffers(9k -> 3k): (sz = 5120)!    
ixgbe: e2b: ** JUMBOMBUF DEBUG ** switching to large buffers(9k -> 3k): (sz = 5120)!    
Ipspace "iwarp-ipspace" created    
WAFL CPLEDGER is enabled. Checklist = 0x7ff841ff    
add host 127.0.10.1: gateway 127.0.20.1    
5    
    You have selected the maintenance boot option:    
    the system has booted in maintenance mode allowing the    
    following operations to be performed:    
    ?                     acorn            
    acpadmin              aggr             
    cna_flash             disk             
    disk_latency          disk_list        
    disk_mung             disk_shelf       
    diskcopy              disktest         
    dumpblock             environment      
    fcadmin               fcstat           
    fctest                fru_led          
    ha-config             halt             
    help           &