AMDU是Oracle 11g里自带的一个免费的工具，用于分析ASM磁盘组的元数据以及从不能mount的磁盘组中往外抽取数据文件。
“NOTE:553639.1 Placeholder for AMDU binaries and using with ASM 10g”明确指出：AMDU也可用于10g，并提供了可用于10g的AMDU的各个操作系统的版本供大家
下载。
AMDU的原理是解析file directory，这一点ODU也是一样，只不过ODU做的更彻底一些，即使file directory全部损坏，ODU也可以把数据文件抽取出来，尽最大的可能挽救用户的数据。
我们来看一个用AMDU从不能mount的磁盘组中往外抽取数据文件的实例：
[root@bspdev odu]# su – oracle
[oracle@bspdev ~]$ sqlplus ‘/ as sysdba’;
SQL*Plus: Release 11.2.0.1.0 Production on Thu Feb 23 10:43:36 2012
Copyright (c) 1982, 2009, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 – Production
With the Partitioning, Automatic Storage Management, OLAP, Data Mining
and Real Application Testing options
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> exit
Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 – Production
With the Partitioning, Automatic Storage Management, OLAP, Data Mining
and Real Application Testing options
[oracle@bspdev ~]$ su – grid
Password:
[grid@bspdev ~]$ sqlplus ‘/ as sysasm’;
SQL*Plus: Release 11.2.0.1.0 Production on Thu Feb 23 10:45:05 2012
Copyright (c) 1982, 2009, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 – Production
With the Automatic Storage Management option
SQL> shutdown immediate
ASM diskgroups dismounted
ASM instance shutdown
SQL> exit
Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 – Production
With the Automatic Storage Management option
[grid@bspdev ~]$ crsctl status res
NAME=ora.DATA.dg
TYPE=ora.diskgroup.type
TARGET=OFFLINE
STATE=OFFLINE
NAME=ora.LISTENER.lsnr
TYPE=ora.listener.type
TARGET=ONLINE
STATE=ONLINE on bspdev
NAME=ora.RECO.dg
TYPE=ora.diskgroup.type
TARGET=OFFLINE
STATE=OFFLINE
NAME=ora.asm
TYPE=ora.asm.type
TARGET=OFFLINE
STATE=OFFLINE
NAME=ora.cssd
TYPE=ora.cssd.type
TARGET=ONLINE
STATE=ONLINE on bspdev
NAME=ora.diskmon
TYPE=ora.diskmon.type
TARGET=ONLINE
STATE=ONLINE on bspdev
NAME=ora.ora11g.db
TYPE=ora.database.type
TARGET=OFFLINE
STATE=OFFLINE
在ASM diskgroup不能mount的情况下asmcmd不能使用：
[grid@bspdev ~]$ asmcmd
Connected to an idle instance.
ASMCMD> ls
ASMCMD-08102: no connection to ASM; command requires ASM to run
但此时ODU内嵌的asmcmd是可以使用的，所以我们可以轻易的使用ODU内嵌的asmcmd命令来得到所有的datafile的名称：
[grid@bspdev ~]$ su -
Password:
[root@bspdev ~]# cd /u01/app/oracle/odu
[root@bspdev odu]# ./odu
Oracle Data Unloader:Release 4.2.1
loading default config…….
byte_order little
block_size 8192
block_buffers 1024
db_timezone -7
Invalid db timezone:-7
client_timezone 8
Invalid client timezone:8
asmfile_extract_path /odu