Most of the time, because ASM does not start properly, data loss is caused. Here are two ways to retrieve data files from ASM
I. Using the AMDU tool
Amdu is a free tool in Oracle 11g that analyzes the metadata of the ASM Disk group and extracts data files from a disk group that cannot be mount "note:553639.1 placeholder for AMDU binaries and Using with ASM 10g "clearly stated: Amdu can also be used for 10g and provides a version of the various operating systems available for use in 10g amdu for everyone to download."
1. Set Ld_library_path
Rac1-> Export LD_LIBRARY_PATH=/TMP/AMDU
2. View ASM Disk Information
rac1->./amdu-diskstring '/dev/raw/raw* '
amdu_2012_03_05_03_17_19/
Rac1-> CD amdu_2012_03_05_03_17_19/
Rac1-> ls
Report.txt
rac1-> more Report.txt
-*-amdu-*-
Amdu Settings ********************************
Oracle_home =/u01/app/oracle/product/10.2.0/db_1
System Name:linux
Node NAME:RAC1
Release:2.6.9-89.0.0.0.1.elhugemem
Version: #1 SMP Tue may 04:38:38 EDT 2009
machine:i686
Amdu run:05-mar-12 03:17:19
Endianess:1
---------------------------------Operations---------------------------------
More Wonderful content: http://www.bianceng.cn/database/Oracle/
-------------------------------Disk Selection-------------------------------
-diskstring '/dev/raw/raw* '
------------------------------Reading Control-------------------------------
-------------------------------Output Control-------------------------------
DISCOVERY **********************************
-----------------------------DISK N0001------------------------------
Disk Path:/dev/raw/raw23
Unique Disk ID:
Disk Label:
Physical Sector size:512 bytes
Disk size:156 Megabytes
* * Not A VALID ASM DISK HEADER. Bad VALUE in FIELD blksize_kfdhdb * *
-----------------------------DISK N0002------------------------------
Disk Path:/DEV/RAW/RAW11
Unique Disk ID:
Disk Label:
Physical Sector size:512 bytes
Disk size:156 Megabytes
* * Not A VALID ASM DISK HEADER. Bad VALUE in FIELD blksize_kfdhdb * *
-----------------------------DISK N0003------------------------------
Disk Path:/dev/raw/raw32
Unique Disk ID:
Disk Label:
Physical Sector size:512 bytes
Disk size:156 Megabytes
* * Not A VALID ASM DISK HEADER. Bad VALUE in FIELD blksize_kfdhdb * *
-----------------------------DISK N0004------------------------------
Disk Path:/dev/raw/raw31
Unique Disk ID:
Disk Label:
Physical Sector size:512 bytes
Disk size:156 Megabytes
* * Not A VALID ASM DISK HEADER. Bad VALUE in FIELD blksize_kfdhdb * *
-----------------------------DISK N0005------------------------------
Disk Path:/dev/raw/raw12
Unique Disk ID:
Disk Label:
Physical Sector size:512 bytes
Disk size:156 Megabytes
* * Not A VALID ASM DISK HEADER. Bad VALUE in FIELD blksize_kfdhdb * *
-----------------------------DISK N0006------------------------------
Disk Path:/DEV/RAW/RAW2
Unique Disk ID:
Disk Label:
Physical Sector size:512 bytes
Disk size:1976 Megabytes
Group Name:data
Disk name:data_0001
Failure Group name:data_0001
Disk number:1
Header Status:3
Disk Creation Time:2012/03/01 22:32:39.289000
Last Mount time:2012/03/05 02:10:02.771000
Compatibility version:0x0a100000
Disk Sector size:512 bytes
Disk size in aus:1976 AUs
Group redundancy:1
Metadata block size:4096 bytes
AU size:1048576 bytes
stride:113792 AUs
Group Creation Time:2012/03/01 22:32:39.221000
File 1 Block 1 Location:au 0
-----------------------------DISK N0007------------------------------
Disk Path:/DEV/RAW/RAW1
Unique Disk ID:
Disk Label:
Physical Sector size:512 bytes
Disk size:3137 Megabytes
Group Name:data
Disk name:data_0000
Failure Group name:data_0000
Disk number:0
Header Status:3
Disk Creation Time:2012/03/01 22:32:39.289000
Last Mount time:2012/03/05 02:10:02.771000
Compatibility version:0x0a100000
Disk Sector size:512 bytes
Disk size in aus:3137 AUs
Group redundancy:1
Metadata block size:4096 bytes
AU size:1048576 bytes
stride:113792 AUs