在11g的asm中增加了md_backup和md_restore命令,用来备份和还原asm的元数据信息
当前磁盘组相关信息

SQL> select PATH,b.NAME from v$asm_disk a,v$asm_diskgroup b where a.GROUP_NUMBER=b.GROUP_NUMBER;
PATH                                     NAME
---------------------------------------- ----------
/dev/oracleasm/disks/VOL2                DATA
/dev/oracleasm/disks/VOL1                DATA
/dev/oracleasm/disks/VOL4                XIFENFEI
/dev/oracleasm/disks/VOL3                XIFENFEI

md_backup操作

--备份所有mount磁盘组
ASMCMD> md_backup /tmp/xifenfei.md
Disk group metadata to be backed up: DATA
Disk group metadata to be backed up: XIFENFEI
Current alias directory path: XFF/ARCHIVELOG
Current alias directory path: XFF/ARCHIVELOG/2012_04_30
Current alias directory path: XFF/ONLINELOG
Current alias directory path: rac-cluster/OCRFILE
Current alias directory path: XFF/ARCHIVELOG/2012_05_01
Current alias directory path: XFF/CONTROLFILE
Current alias directory path: XFF/ARCHIVELOG/2012_04_13
Current alias directory path: rac-cluster/ASMPARAMETERFILE
Current alias directory path: rac-cluster
Current alias directory path: XFF
Current alias directory path: XFF/ARCHIVELOG/2012_03_03
Current alias directory path: XFF/PARAMETERFILE
Current alias directory path: XFF/DATAFILE
Current alias directory path: ASM/DATAFILE
Current alias directory path: XFF/CONTROLFILE
Current alias directory path: XFF
Current alias directory path: XFF/ONLINELOG
Current alias directory path: XFF/TEMPFILE
Current alias directory path: ASM
--备份指定磁盘组
ASMCMD> md_backup /tmp/xifenfei_data.md -G DATA
Disk group metadata to be backed up: DATA
Current alias directory path: XFF/ARCHIVELOG/2012_03_03
Current alias directory path: XFF/CONTROLFILE
Current alias directory path: XFF/ARCHIVELOG/2012_05_01
Current alias directory path: XFF/ARCHIVELOG
Current alias directory path: rac-cluster/OCRFILE
Current alias directory path: XFF/ARCHIVELOG/2012_05_24
Current alias directory path: XFF/ONLINELOG
Current alias directory path: XFF/ARCHIVELOG/2012_04_30
Current alias directory path: rac-cluster/ASMPARAMETERFILE
Current alias directory path: rac-cluster
Current alias directory path: XFF
Current alias directory path: XFF/ARCHIVELOG/2012_04_13

md_restore操作

--生产sql文件(未执行)
ASMCMD> md_restore -S  /tmp/get_dg_sql -G data /tmp/xifenfei_data.md
Current Diskgroup metadata being restored: DATA
破坏XIFENFEI磁盘组中的其中一个asm disk(/dev/oracleasm/disks/VOL3)
[root@rac1 tmp]#  dd if=/dev/zero of=/dev/sdb1 bs=4096 count=1
1+0 records in
1+0 records out
4096 bytes (4.1 kB) copied, 4.8629e-05 seconds, 84.2 MB/s
--尝试还原磁盘组(操作单位是磁盘组)
ASMCMD>  md_restore /tmp/xifenfei.md --silent -G xifenfei
Current Diskgroup metadata being restored: XIFENFEI
ASMCMD-9352: CREATE DISKGROUP failed
ORA-15018: diskgroup cannot be created
ORA-15033: disk /dev/oracleasm/disks/VOL4 belongs to diskgroup "XIFENFEI" (DBD ERROR: OCIStmtExecute)
--如果一个磁盘组中某个asm disk 出了问题,这种方法不能生效,甚至需要先dd 处理掉所有该磁盘组中的asm disk

总结说明
md_backup和md_restore是磁盘组级别的备份和还原,如果一个磁盘组的某个asm disk出现问题,使用这对命令解决起来还是很麻烦,甚至根本不可行(因为代价太大:要删除该磁盘组其他asm disk header,然后要重新还原所有数据文件),这样的情景下dd或者kfed的备份还是非常有必要,ASM DISK HEADER 备份与恢复.如果是一个磁盘组都损坏,需要还原磁盘组,这个时候这个命令非常的完美(至少比起dd和kfed方便很多).md_backup/md_restore和dd与kfed是互补的命令,而不是md_backup/md_restore出现使得dd和kfed在asm元数据的备份恢复上就没有用武之地.