In a previous post, I explained how to dump ASM Disk header and how to analyze it. This method, which used kfed binary, is a little bit complex because of fields with a complex name extracted from the internal structure.
Another way to proceed and to see main information about asm disks is to use an undocumented binary located in $ORACLE_HOME/bin named amdu.
If amdu is not available in your $ORACLE_HOME/bin directory, you can build it with the next make command:
[oracle@oel ~]$ make -f $ORACLE_HOME/rdbms/lib/ins_rdbms.mk iamdu
To dump your ASM diskheader, you just have to execute this command with the -diskstring option and specify the location of your ASM disk devices (default uses ASM lib directory):
[oracle@oel ~]$ amdu -diskstring='/dev/oracleasm/disks/*'
amdu_2012_03_21_11_14_36/
Now, change directory to the output generated and have a look to the report.txt file:
[oracle@oel ~]$ cd amdu_2012_03_21_11_14_36/
[oracle@oel amdu_2012_03_21_11_14_36]$ cat report.txt
-*-amdu-*-
******************************* AMDU Settings ********************************
ORACLE_HOME = /u01/app/oracle/product/11.2.0.3/dbhome_1
System name: Linux
Node name: oel
Release: 2.6.18-274.18.1.0.1.el5
Version: #1 SMP Thu Feb 9 19:07:16 EST 2012
Machine: x86_64
amdu run: 21-MAR-12 11:14:36
Endianess: 1
--------------------------------- Operations ---------------------------------
------------------------------- Disk Selection -------------------------------
-diskstring '/dev/oracleasm/disks/*'
------------------------------ Reading Control -------------------------------
------------------------------- Output Control -------------------------------
********************************* DISCOVERY **********************************
----------------------------- DISK REPORT N0001 ------------------------------
Disk Path: /dev/oracleasm/disks/ASM1
Unique Disk ID:
Disk Label:
Physical Sector Size: 512 bytes
Disk Size: 1019 megabytes
Group Name: DATA
Disk Name: DATA_0000
Failure Group Name: DATA_0000
Disk Number: 0
Header Status: 3
Disk Creation Time: 2011/05/27 10:57:54.822000
Last Mount Time: 2012/03/21 08:54:10.221000
Compatibility Version: 0x0b200000(11020000)
Disk Sector Size: 512 bytes
Disk size in AUs: 1019 AUs
Group Redundancy: 1
Metadata Block Size: 4096 bytes
AU Size: 1048576 bytes
Stride: 113792 AUs
Group Creation Time: 2011/05/27 10:57:54.456000
File 1 Block 1 location: AU 2
OCR Present: NO
----------------------------- DISK REPORT N0002 ------------------------------
Disk Path: /dev/oracleasm/disks/ASM2
Unique Disk ID:
Disk Label:
Physical Sector Size: 512 bytes
Disk Size: 1019 megabytes
Group Name: DATA
Disk Name: DATA_0001
Failure Group Name: DATA_0001
Disk Number: 1
Header Status: 3
Disk Creation Time: 2011/05/27 10:57:54.822000
Last Mount Time: 2012/03/21 08:54:10.221000
Compatibility Version: 0x0b200000(11020000)
Disk Sector Size: 512 bytes
Disk size in AUs: 1019 AUs
Group Redundancy: 1
Metadata Block Size: 4096 bytes
AU Size: 1048576 bytes
Stride: 113792 AUs
Group Creation Time: 2011/05/27 10:57:54.456000
File 1 Block 1 location: AU 0
OCR Present: NO
******************************* END OF REPORT ********************************
As mentioned, now you know if your disk is part of a disk group, the DG Allocation Unit size, disk size, last mounted time etc.
Of course, this tool can be used regarless of the asm instance status.
Data ... as usual 