近日遇到一个问题，就是asm diskgroup无法挂载，通过分析之后，发现有会快存在，，但是由于没有备份，没有办法重建diskgroup并从backup恢复--所以所以所以....备份很重要啊！不然，哭！！是早晚的事情！
通过解决这个问题，我在自己的测试环境测试了如何在asm diskgroup无法mount的情况下，尽量挽救数据文件。
这里使用到oracle 工具amdu，该具体信息可以参考amdu functionality and usage (doc id 855791.1)
1. 由于diskgroup无法挂载，spfile、controlfile、datafile都无法读取
根据步骤，我们首先需要恢复spfile文件，spfile文件存在的意义就是找到control_files的位置，如果spfile无法访问，需要查找备份。
sql> show parameter control_files+data/db/controlfile/current.260.804295233, +fra/db/controlfile/current.256.804295237
2. 通过asm实例找到asm_diskstring
sql> show parameter disknametypevalue------------------------------------ ----------- ------------------------------asm_diskgroupsstringdata, fraasm_diskstringstring/dev/sd*
3. 查找asm disk的路径，后续要指定diskstring来扫描磁盘
sql> select name,state,type,offline_disks,voting_files from v$asm_diskgroup;sql> col path for a50 sql> col name for a10 sql> set line 200 sql> select disk_number,group_number,path,name from v$asm_disk;disk_number group_number pathname----------- ------------ -------------------------------------------------- ----------12 /dev/oracleasm/disks/asmdisk5fra_000102 /dev/oracleasm/disks/asmdisk4fra_000021 /dev/oracleasm/disks/asmdisk3data_0002disk_number group_number pathname----------- ------------ -------------------------------------------------- ----------11 /dev/oracleasm/disks/asmdisk2data_000101 /dev/oracleasm/disks/asmdisk1data_0000
4. 在diskgroup mount状态，是不能使用amdu导出文件的
执行amdu命令开始导出，遇到错误
$ amdu -diskstring '/dev/oracleasm/disks/asmdisk*' -extract data.260amdu_2013_07_03_17_29_13/amdu-00204: disk n0005 is in currently mounted diskgroup dataamdu-00201: disk n0005: '/dev/oracleasm/disks/asmdisk1'
检查发现磁盘组mount
$ crsctl status res -t--------------------------------------------------------------------------------nametarget stateserverstate_details--------------------------------------------------------------------------------ora.data.dgonline onlinesingle-dbora.fra.dgonline onlinesingle-db
5. 导出控制文件
$ amdu -diskstring '/dev/oracleasm/disks/asmdisk*' -extract data.260amdu_2013_07_03_17_46_07/[oracle@single-db amdu]$ cd amdu_2013_07_03_17_46_07/[oracle@single-db amdu_2013_07_03_17_46_07]$ lsdata_260.f report.txt
6. 尝试挂载control file
发现spfile也存放在磁盘组中无法nomount
$ sqlplus / as sysdbasql> startup nomount;ora-01078: failure in processing system parametersora-01565: error in identifying file '+data/db/spfiledb.ora'ora-17503: ksfdopn:2 failed to open file +data/db/spfiledb.oraora-15056: additional error messageora-17503: ksfdopn:dgopenfile05 failed to open file +data/db/spfiledb.oraora-17503: ksfdopn:2 failed to open file +data/db/spfiledb.oraora-15001: diskgroup data does not exist or is not mountedora-06512: at line 4
7. 那就编辑一个新的pfile文件
$ cp init.ora spfilebk.ora$ vi spfilebk.ora~~~~~~~~~~~~~~~db_name='db'sga_target=1gprocesses = 150audit_trail ='db'db_block_size=8192db_domain=''db_recovery_file_dest_size=2gopen_cursors=300remote_login_passwordfile='exclusive'undo_tablespace='undotbs1'control_files = /u01/amdu/amdu_2013_07_03_17_46_07/data_260.fcompatible ='11.2.0'~~~~~~~~~~~~~~~
8. 通过导出的控制文件启动数据库到mount模式，成功启动，说明amdu导出的数据时正确的，继续。。。。。
$ sqlplus / as sysdbasql> startup nomount pfile='/u01/app/oracle/product/11.2.0/dbhome_1/dbs/spfilebk.ora';oracle instance started.total system global area 1068937216 bytesfixed size2220200 bytesvariable size281022296 bytesdatabase buffers780140544 bytesredo buffers5554176 bytessql> alter database mount;database altered.
9. 查看数据文件的位置，然后一一导出
sql> select name from v$datafile;name--------------------------------------------------------------------------------+data/db/datafile/system.256.804295135+data/db/datafile/sysaux.257.804295137+data/db/datafile/undotbs1.258.804295139+data/db/datafile/users.259.804295141$ amdu -diskstring '/dev/oracleasm/disks/asmdisk*' -extract data.256
10. 重命名数据文件，并移动到同一个目录下，准备挂载数据文件
$ mv amdu_2013_07_03_18_12_56/data_257.f sysaux.257.804295137$ mv amdu_2013_07_03_18_22_23/data_259.f users.259.804295141$ mv amdu_2013_07_03_18_23_06/data_258.f undotbs1.258.804295139$ ll-rw-r--r-- 1 oracle dba 545267712 jul 3 18:14 sysaux.257.804295137-rw-r--r-- 1 oracle dba 702554112 jul 3 18:11 system.256.804295135-rw-r--r-- 1 oracle dba 99622912 jul 3 18:23 undotbs1.258.804295139-rw-r--r-- 1 oracle dba 5251072 jul 3 18:22 users.259.804295141
11. 挂载前需要修改pfile文件，下面是open数据库是control file如何识别不同路径的datafile， 我使用convert参数来解决（也可以是用set newname的方式）
db_file_name_convert='+data/db/datafile','/u01/amdu/amdu_datafile'
添加完pfile，启动数据库，最终成功启动数据库