Skip to content

Oracle恢复

OBJ$表上索引有坏块导致部分业务失效的修复

这种问题的解决办法有好几种,根据数据量的大小以及业务是否允许停机的情况考虑,主要分以下几类救急办法:

一、坏块在索引上的位置判断

1.1如果坏块不多,而且坏块都在在索引比较靠前的位置(这个靠前的位置每个版本不一样,每个版本的对象数不一样),可以理解为在建库时候obj$自带索引的那个块最大地址就是属于考前的位置,当坏块在这个位置前面时候有一种比较便捷的处理方式,

就是通过创建一个一模一样的数据库,使用bbed copy(相比DD操作,操作起来超级简单又不容易出错)把对应坏块位置的块copy覆盖损坏的块,apply后即可(如果是在obj$表中的块那么记得修改下obj里对应的create time即可使数据库恢复正常,这个在前面有个案例描述过)。

 

1.2如果坏块是在索引靠后的位置或者坏块很多,索引的对象为后面创建的对象,那么这个时候就比较麻烦了,好在obj$的数据是完整的,

我的建议是采用2种方法,

1.2.1  采用屏蔽obj$索引的方法,具体需要修改基表,这个方法在前面文章中有描述。这个情况一般用在数据库比较大,比如数据量有几十个T,上百T或者业务不能接受长时间停机的情况

1.2.2 当数据库的数据量不大的时候,可以采用另外一种办法,使用exp来导出数据进行修复,一般这个时候exp工具是无法直接使用的,需要使用到catexp.sql这个脚本,具体的方法请查阅博客里的文章 Corruptions on OBJ$ indexes

 

What is bootstrap?

Bootstrap is a technique for loading the first few instructions of a computer program into active memory and then using them to bring in the rest of the program.

What is bootstrap in Oracle ?

In Oracle, Bootstrap refers to loading of metadata (data dictionary) before we OPEN the database.Bootstrap objects are classified as the objects (tables / indexes / clusters) with the object_id below 56 as bootstrap objects.  These objects are mandatory to bring up an instance, as this contains the most important metadata of the database.

What happens on database startup?

This shall be explained by setting the SQL_TRACE while opening the database.Connect as sysdba and do the following
SQL> startup mount ;
SQL> alter session set events ‘10046 trace name context forever, level 12 ‘ ;
SQL> alter database open ;
SQL>  alter session set events ‘10046 trace name context off ‘ ;
SQL> ORADEBUG SETMYPID
SQL> ORADEBUG TRACEFILE_NAME
The sql_trace of the above process explains the following operations behind startup. The bootstrap operation happens between MOUNT stage and OPEN stage.
1.)  The first SQL after in the above trace shows the creation of the bootstrap$ table. Something similar to the following:
create table bootstrap$ ( line# number not null, obj# number not null, sql_text varchar2(4000) not null) storage (initial 50K objno 56 extents (file 1 block 377))
This sys.bootstrap$ table contains the DDL’s for other bootstrap tables (object_id below 56). Actually these tables were created internally by the time of database creation (by sql.bsq), The create DDL passed between MOUNT and OPEN stage will be executed through different driver routines. In simple words these are not standard CREATE DDLs.
While starting up the database oracle will load these objects into memory (shared_pool), (ie) it will assign the relevant object number and refer to the datafile and the block associated with that. And such operations happen only while warm startup.
 The internals of the above explained in ‘kqlb.c’.
2.)  Now a query executed against the sys.bootstrap$ table, which holds the create sql’s for other base tables.
select line#, sql_text from bootstrap$ where obj# != :1 (56)
Subsequently it will create those objects by running those queries.
Object number 0 – (System Rollback Segment)
Object number 2 to 55 (Other base tables)
Object number 1 is NOT used by any of the objects.
3.) Performs various operations to keep the bootstrap objects in consistent state.
Upon the successful completion of bootstrap the database will do the other tasks like recovery and will open the database.

Which objects are classified as bootstrap objects in oracle database?

Objects with data_object_id less than 56 are classified as core bootstrap objects.The objects are added to the bootstrap. The objects affected are :

hist_head$
histgrm$
i_hh_obj#_col#
i_hh_obj#_intcol#
i_obj#_intcol#
i_h_obj#_col#
c_obj#_intcol#
From 10.1 the following objects have been added:
fixed_obj$
tab_stats$
ind_stats$
i_fixed_obj$_obj#
i_tab_stats$_obj#
i_ind_stats$_obj#
object_usage
These additional objects shall be re-classified (or) ignored by following methods.
1. Opening the database in migrate mode
2. Using event 38003
Event 38003 affects the bootstrap process of loading the fixed cache in  kqlblfc(). Per default certain objects are marked as bootstrap objects (even though they are not defined as such in sys.bootstrap$) but by setting the event they will be left as non-bootstrapped.

What is bootstrap process failure? or  ORA-00704

This ORA-00704 error SERIOUS if reported at startup. This error refers to some problem during bootstrap operation. Any ORA-00704 error on STARTUP / RECOVER is serious, this error normally rose due to some inconsistency with the bootstrap segments (or) data corruption on bootstrap$ (or) any of the base tables below object_id  56. After this error it might not allow to open that database.

When ORA-00704 shall occur?

1. There is a probable of this error when any unsupported operations are tried to force open the database.
2. This error can also occur when system datafile has corrupted blocks. (ORA-01578)
3. In earlier releases of oracle (prior to 7.3.4 and 8.0.3) this issue shall arise due to Bug 434596
The option is to restore it from a good backup and recover it.
-> If the underlying cause is physical corruption that is due to hardware problems then do complete recovery.
-> If the issue is not relating to any physical corruption, then the problem could be due some unsupported actions on Bootstrap, and a Point In Time Recovery would be an option in such cas.
Oracle bootstrap$ E版解释

Corruptions on OBJ$ indexes。OBJ$上索引损坏的一种处理方式(数据量不大的时候,只要业务允许停机可以忽略数据量的考虑)

INTERNAL:Corruptions on OBJ$ indexes (Doc ID 39400.1)

 

To export a system when there are corruptions on indexes on OBJ$:

 

–     Take a FULL COLD BACKUP

 

–     Connect internal in SQLDBA and assuming your default tablespace is

SYSTEM and you have some free space:

 

create table pig$ as select * from obj$;

 

create unique index p_obj1 on pig$(obj#);

 

create unique index p_obj2 on pig$(owner#, name, namespace,

remoteowner, linkname);

 

 

–     Now edit the catexp.sql script (take a safe copy first).

This is generally located in the RDBMS/ADMIN directory.

 

Edit this to change ALL references to the table ‘OBJ$’

to now reference ‘PIG$’.

 

–     Connect internal in SQLDBA and run this new CATEXP.SQL

 

–     Perform a FULL export.

 

–     Shutdown the database and delete it.

 

–     Recreate the database from scratch with a CREATE DATABASE command.

Ensure you set up a second rollback segment for non-system

tablespace use on the import.

 

–     Perform a FULL import.

sysaux表空间损坏导致db无法open的故障修复–重建sysaux 表空间

某政府机关核心数据库sysaux表空间由于光纤链路问题出现损坏导致数据库无法open,通过特殊的办法修复,后续补上.

 

该问题为重建sysaux的过程,主要sysaux表空被截断了,文件大小不对.所以采用重建的办法.主要步骤如下:

 

1.用exp基于表空间的方式备份数据

2.查询当前数据库有多少组件

3.删掉sysaux表空间

4.卸载相关组件

5.重建sysaux表空间

6.重装组件

7.expdp导出全库重建整个库.

 

将该SYSAUX 数据文件 offline 后启动实例到 open 状态

 

SQL> alter database datafile 3 offline drop;Database altered.
SQL> alter database open;

Database altered.

SQL> select status from dba_tablespaces where tablespace_name=’SYSAUX’;

STATUS ——— ONLINE

SQL> select file_name,status,online_status from tablespace_name=’SYSAUX’;

FILE_NAME ——————————————————————————–STATUS ——— ——-

===该部分作者加密===

SQL> alter session set events ‘25475 trace name context off’; Session altered.

安装该组件

SQL> @?/rdbms/admin/owminst.plb

测试 exp 导出已经可执行

 

重建 DB CONTROL

 

SYSMAN需要删掉。

 

SQL>alter session set events ‘25475 trace name context forever, level 2’;
Session altered.
SQL> drop user sysman cascade;

User dropped.
SQL> alter session set events ‘25475 trace name context off’;
Session altered.
SQL> @?/sysman/admin/emdrep/sql/emreposcre ?/ SYSMAN luda TEMP ON;

 

重建 OLAP

[oracle@rac ~]$ cd $ORACLE_HOME/olap/admin

SQL> @catnoamd.sql

SQL> @olapidrp.plb

SQL> @catnoaps.sql

SQL> @catnoxoq.sql

SQL> @cwm2drop.sql

SQL> @?/olap/admin/olap.sql SYSAUX TEMP;

安装 Oracle Spatial

SQL> @?/md/admin/mdinst.sql;

安装 TX

SQL> @?/ctx/admin/catctx luda SYSAUX TEMP NOLOCK;

SQL> conn CTXSYS/luda
SQL> @?/ctx/admin/defaults/dr0defin.sql “AMERICAN”

安装 XML

SQL> conn / as sysdba
SQL> @?/rdbms/admin/catqm.sql luda SYSAUX TEMP;

SQL> @?/rdbms/admin/catxdbj.sql;
SQL> @?/rdbms/admin/catrul.sql;

安装 TEXT

SQL> @?/ctx/admin/catctx aaa SYSAUX TEMP NOLOCK; SQL> conn CTXSYS/luda
SQL> @?/ctx/admin/defaults/dr0defin.sql “AMERICAN”

安装 Oracle Intermedia
SQL> @?/ord/admin/ordinst.sql SYSAUX SYSAUX;

SQL> @?/ord/im/admin/iminst.sql;

 

unused column 和 drop column操作实质

unused column和drop column的操作从本质上讲是不一样的,unused是通过变更数据字典的信息让sql无法访问到column,而drop是直接在物理数据层做了变动。这里的操作后台跟踪可以用event 10046去验证,这里不做描述.

下面通过实验的方式验证unused和drop column的操作对比情况:

1.创建测试表

SQL> grant dba to luda;

Grant succeeded.

SQL> conn luda/luda
Connected.


SQL> create table luda_t1 as  select * from dba_objects;

Table created.

SQL> set timing on
SQL> set serverout on
SQL> exec showspace('LUDA_T1','LUDA')
Total Blocks............................768
Total Bytes.............................6291456
Unused Blocks...........................53
Unused Bytes............................434176
Last Used Ext FileId....................4
Last Used Ext BlockId...................2953
Last Used Block.........................75
*************************************************
The segment is analyzed
0% -- 25% free space blocks.............0
0% -- 25% free space bytes..............0
25% -- 50% free space blocks............0
25% -- 50% free space bytes.............0
50% -- 75% free space blocks............0
50% -- 75% free space bytes.............0
75% -- 100% free space blocks...........0
75% -- 100% free space bytes............0
Unused Blocks...........................0
Unused Bytes............................0
Total Blocks............................695
Total bytes.............................5693440

PL/SQL procedure successfully completed.

Elapsed: 00:00:00.00
SQL> select b.name,a.value from v$mystat a,v$statname b where a.statistic#=b.statistic# and b.name='redo size';

NAME                                                                  VALUE
---------------------------------------------------------------- ----------
redo size                                                             80916

Elapsed: 00:00:00.01
SQL> select b.name,a.value from v$mystat a,v$statname b where a.statistic#=b.statistic# and b.name='undo change vector size';

NAME                                                                  VALUE
---------------------------------------------------------------- ----------
undo change vector size                                               21012

Elapsed: 00:00:00.00

2.设置object_name为unused

SQL> alter table luda_t1 set unused column object_name;

Table altered.

Elapsed: 00:00:00.02
SQL> exec showspace('LUDA_T1','LUDA')  ---- 对比操作前,可以发现luda_t1表存储信息未有变动
Total Blocks............................768
Total Bytes.............................6291456
Unused Blocks...........................53
Unused Bytes............................434176
Last Used Ext FileId....................4
Last Used Ext BlockId...................2953
Last Used Block.........................75
*************************************************
The segment is analyzed
0% -- 25% free space blocks.............0
0% -- 25% free space bytes..............0
25% -- 50% free space blocks............0
25% -- 50% free space bytes.............0
50% -- 75% free space blocks............0
50% -- 75% free space bytes.............0
75% -- 100% free space blocks...........0
75% -- 100% free space bytes............0
Unused Blocks...........................0
Unused Bytes............................0
Total Blocks............................695
Total bytes.............................5693440

PL/SQL procedure successfully completed.

Elapsed: 00:00:00.01
SQL> select b.name,a.value from v$mystat a,v$statname b where a.statistic#=b.statistic# and b.name='redo size';

NAME                                                                  VALUE
---------------------------------------------------------------- ----------
redo size                                                             92176

Elapsed: 00:00:00.00

---产生了少量redo日志

SQL> select b.name,a.value from v$mystat a,v$statname b where a.statistic#=b.statistic# and b.name='undo change vector size';

NAME                                                                  VALUE
---------------------------------------------------------------- ----------
undo change vector size                                               25212

Elapsed: 00:00:00.00

--产生了少量undo

3.执行drop unused column

SQL> alter table luda_t1 drop unused column;

Table altered.

Elapsed: 00:00:00.26
SQL> exec showspace('LUDA_T1','LUDA') --对比操作前可以发现在freespace层面25%-50%多出了642的block
Total Blocks............................768
Total Bytes.............................6291456
Unused Blocks...........................53
Unused Bytes............................434176
Last Used Ext FileId....................4
Last Used Ext BlockId...................2953
Last Used Block.........................75
*************************************************
The segment is analyzed
0% -- 25% free space blocks.............0
0% -- 25% free space bytes..............0
25% -- 50% free space blocks............642
25% -- 50% free space bytes.............5259264
50% -- 75% free space blocks............0
50% -- 75% free space bytes.............0
75% -- 100% free space blocks...........0
75% -- 100% free space bytes............0
Unused Blocks...........................0
Unused Bytes............................0
Total Blocks............................53  --总占用block降低为53个,总块数不变642+53=695
Total bytes.............................434176

PL/SQL procedure successfully completed.

Elapsed: 00:00:00.00
SQL>  select b.name,a.value from v$mystat a,v$statname b where a.statistic#=b.statistic# and b.name='redo size';

NAME                                                                  VALUE
---------------------------------------------------------------- ----------
redo size                                                          12393932

--产生大量的redo日志相对比上一次操作的redo量
Elapsed: 00:00:00.01
SQL> select b.name,a.value from v$mystat a,v$statname b where a.statistic#=b.statistic# and b.name='undo change vector size';

NAME                                                                  VALUE
---------------------------------------------------------------- ----------
undo change vector size                                             5128064
--产生大量的undo信息相对比上一次操作的undo量
Elapsed: 00:00:00.00
SQL>

4.执行drop column的测试

SQL> alter table luda_t1 drop column object_type;

Table altered.

Elapsed: 00:00:00.25
SQL> exec showspace('LUDA_T1','LUDA') -- drop 操作效果与drop unused一致,释放空间,降低高水位
Total Blocks............................768
Total Bytes.............................6291456
Unused Blocks...........................53
Unused Bytes............................434176
Last Used Ext FileId....................4
Last Used Ext BlockId...................2953
Last Used Block.........................75
*************************************************
The segment is analyzed
0% -- 25% free space blocks.............0
0% -- 25% free space bytes..............0
25% -- 50% free space blocks............664
25% -- 50% free space bytes.............5439488
50% -- 75% free space blocks............1
50% -- 75% free space bytes.............8192
75% -- 100% free space blocks...........0
75% -- 100% free space bytes............0
Unused Blocks...........................0
Unused Bytes............................0
Total Blocks............................30
Total bytes.............................245760

PL/SQL procedure successfully completed.

Elapsed: 00:00:00.01
SQL>
SQL> select b.name,a.value from v$mystat a,v$statname b where a.statistic#=b.statistic# and b.name='redo size';

NAME                                                                  VALUE
---------------------------------------------------------------- ----------
redo size                                                          23902388
--产生大量的redo日志相对比上一次操作的redo量
Elapsed: 00:00:00.01
SQL> select b.name,a.value from v$mystat a,v$statname b where a.statistic#=b.statistic# and b.name='undo change vector size';
--产生大量的undo信息相对比上一次操作的undo量
NAME                                                                  VALUE
---------------------------------------------------------------- ----------
undo change vector size                                             9439452

Elapsed: 00:00:00.00
SQL>

这里验几个情况:

1.unused column只产生少量的redo和undo,真实在表存储部分并未做变动,高水位线没有变动.真实数据部分并未被oracle处理,而根据trace信息可以发现unused column是在数据字典层面做的变动,对被unused操作的字段打上对于的flag.

2.drop unused column 操作会对被标记为unused flag的数据进行rewrite(trace可以发现)并释放空间,降低高水位,同时产生大量的redo和undo.

3.drop column操作会对整个字段物理数据部分直接进行删除(bbed可以发现),并更新table entries.同时降低高水位产生大量的redo和undo.相当于一次数据重组.

以下的set unused 以及drop column的trace结果图作为参考:

unused_column

drop_column

检测坏块处于对象上面还是空闲空间的脚本

该脚本的作用为查找损坏的块是在对象上面还是在空闲空间上.

set lines 200 pages 10000
col segment_name format a30

SELECT e.owner, e.segment_type, e.segment_name, e.partition_name, c.file#
, greatest(e.block_id, c.block#) corr_start_block#
, least(e.block_id+e.blocks-1, c.block#+c.blocks-1) corr_end_block#
, least(e.block_id+e.blocks-1, c.block#+c.blocks-1)
- greatest(e.block_id, c.block#) + 1 blocks_corrupted
, null description
FROM dba_extents e, v$database_block_corruption c
WHERE e.file_id = c.file#
AND e.block_id <= c.block# + c.blocks - 1
AND e.block_id + e.blocks - 1 >= c.block#
UNION
SELECT s.owner, s.segment_type, s.segment_name, s.partition_name, c.file#
, header_block corr_start_block#
, header_block corr_end_block#
, 1 blocks_corrupted
, 'Segment Header' description
FROM dba_segments s, v$database_block_corruption c
WHERE s.header_file = c.file#
AND s.header_block between c.block# and c.block# + c.blocks - 1
UNION
SELECT null owner, null segment_type, null segment_name, null partition_name, c.file#
, greatest(f.block_id, c.block#) corr_start_block#
, least(f.block_id+f.blocks-1, c.block#+c.blocks-1) corr_end_block#
, least(f.block_id+f.blocks-1, c.block#+c.blocks-1)
- greatest(f.block_id, c.block#) + 1 blocks_corrupted
, 'Free Block' description
FROM dba_free_space f, v$database_block_corruption c
WHERE f.file_id = c.file#
AND f.block_id <= c.block# + c.blocks - 1
AND f.block_id + f.blocks - 1 >= c.block#
ORDER BY file#, corr_start_block#;

测试案例:

构造坏块

RMAN>  blockrecover datafile 4 block 20 clear;

Starting blockrecover at 28-SEP-15
using channel ORA_DISK_1
Finished blockrecover at 28-SEP-15

RMAN>  blockrecover datafile 4 block 22 clear;

Starting blockrecover at 28-SEP-15
using channel ORA_DISK_1
Finished blockrecover at 28-SEP-15

使用rman检测

RMAN> backup validate datafile 4;

Starting backup at 28-SEP-15
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=146 devtype=DISK
channel ORA_DISK_1: starting full datafile backupset
channel ORA_DISK_1: specifying datafile(s) in backupset
input datafile fno=00004 name=/luda/oracle/data/user01.dbf
channel ORA_DISK_1: backup set complete, elapsed time: -01:59:59
Finished backup at 28-SEP-15

执行该脚本查询坏块对应的对象

SQL> select * from v$database_block_corruption ;

     FILE#     BLOCK#     BLOCKS CORRUPTION_CHANGE# CORRUPTIO
---------- ---------- ---------- ------------------ ---------
         4         22          1                  0 CHECKSUM
         4         20          1                  0 CHECKSUM


SQL> set lines 200 pages 10000
SQL> col segment_name format a30
SQL>
SQL> SELECT e.owner, e.segment_type, e.segment_name, e.partition_name, c.file#
  2  , greatest(e.block_id, c.block#) corr_start_block#
  3  , least(e.block_id+e.blocks-1, c.block#+c.blocks-1) corr_end_block#
  4  , least(e.block_id+e.blocks-1, c.block#+c.blocks-1)
  5  - greatest(e.block_id, c.block#) + 1 blocks_corrupted
  6  , null description
  7  FROM dba_extents e, v$database_block_corruption c
  8  WHERE e.file_id = c.file#
  9  AND e.block_id < = c.block# + c.blocks - 1
 10  AND e.block_id + e.blocks - 1 >= c.block#
 11  UNION
 12  SELECT s.owner, s.segment_type, s.segment_name, s.partition_name, c.file#
 13  , header_block corr_start_block#
 14  , header_block corr_end_block#
 15  , 1 blocks_corrupted
 16  , 'Segment Header' description
 17  FROM dba_segments s, v$database_block_corruption c
 18  WHERE s.header_file = c.file#
 19  AND s.header_block between c.block# and c.block# + c.blocks - 1
 20  UNION
 21  SELECT null owner, null segment_type, null segment_name, null partition_name, c.file#
 22  , greatest(f.block_id, c.block#) corr_start_block#
 23  , least(f.block_id+f.blocks-1, c.block#+c.blocks-1) corr_end_block#
 24  , least(f.block_id+f.blocks-1, c.block#+c.blocks-1)
 25  - greatest(f.block_id, c.block#) + 1 blocks_corrupted
 26  , 'Free Block' description
 27  FROM dba_free_space f, v$database_block_corruption c
 28  WHERE f.file_id = c.file#
 29  AND f.block_id < = c.block# + c.blocks - 1
 30  AND f.block_id + f.blocks - 1 >= c.block#
 31  ORDER BY file#, corr_start_block#;

OWNER                          SEGMENT_TYPE       SEGME PARTITION_NAME                      FILE# CORR_START_BLOCK# CORR_END_BLOCK# BLOCKS_CORRUPTED DESCRIPTION
------------------------------ ------------------ ----- ------------------------------ ---------- ----------------- --------------- ---------------- --------------
SYS                            TABLE              LUDA                                          4                20              20                1
SYS                            TABLE              LUDA                                          4                22              22                1

使用kfed修复损坏的asm disk header以及恢复原理测试.(disk header backup in au no.1)

In ASM versions 11.1.0.7 and later, the ASM disk header block is backed up in the second last ASM metadata block in the allocation unit 1.
Kfed parameters

aun – Allocation Unit (AU) number to read from. Default is AU0, or the very beginning of the ASM disk.
aus – AU size. Default is 1048576 (1MB). Specify the aus when reading from a disk group with non-default AU size.
blkn – block number to read. Default is block 0, or the very first block of the AU.
dev – ASM disk or device name. Note that the keyword dev can be omitted, but the ASM disk name is mandatory.
Understanding ASM disk layout

Read ASM disk header block from AU[0]

[root@grac41 Desktop]# kfed read  /dev/asm_test_1G_disk1 | egrep 'name|size|type'
kfbh.type:                            1 ; 0x002: KFBTYP_DISKHEAD   <-- ASM disk header
kfdhdb.dskname:               TEST_0000 ; 0x028: length=9          <-- ASM disk name
kfdhdb.grpname:                    TEST ; 0x048: length=4          <-- ASM DG name
kfdhdb.fgname:                TEST_0000 ; 0x068: length=9          <-- ASM Failgroup
kfdhdb.capname:                         ; 0x088: length=0
kfdhdb.secsize:                     512 ; 0x0b8: 0x0200            <-- Disk sector size
kfdhdb.blksize:                    4096 ; 0x0ba: 0x1000            <-- ASM block size
kfdhdb.ausize:                  1048576 ; 0x0bc: 0x00100000        <-- AU size : 1 Mbyte
kfdhdb.dsksize:                    1023 ; 0x0c4: 0x000003ff        <-- ASM disk size : 1 GByte

Check ASM block types for the first 2 AUs
AU[0] :

[root@grac41 Desktop]# kfed find /dev/asm_test_1G_disk1
Block 0 has type 1
Block 1 has type 2
Block 2 has type 3
Block 3 has type 3
Block 4 has type 3
Block 5 has type 3
Block 6 has type 3
Block 7 has type 3
Block 8 has type 3
Block 9 has type 3
Block 10 has type 3
..
Block 252 has type 3
Block 253 has type 3
Block 254 has type 3
Block 255 has type 3

AU[1] :

[root@grac41 Desktop]#  kfed find /dev/asm_test_1G_disk1 aun=1
Block 256 has type 17
Block 257 has type 17
Block 258 has type 13
Block 259 has type 18
Block 260 has type 13
..
Block 508 has type 13
Block 509 has type 13
Block 510 has type 1
Block 511 has type 19

Summary :

–> Disk header size is 512 bytes
AU size = 1Mbyte –> AU block size = 4096
This translates to 1048576 / 4096 = 256 blocks to read an AU ( start with block 0 – 255 )
Block 510 and block 0 storing an ASM disk header ( == type 1 )

Run the kfed command below if you interested in a certain ASM block type ( use output from kfed find to the type info )
[root@grac41 Desktop]# kfed read /dev/asm_test_1G_disk1 aun=1 blkn=255 | egrep ‘type’
kfbh.type: 19 ; 0x002: KFBTYP_HBEAT

Some ASM block types

[root@grac41 Desktop]# kfed read  /dev/asm_test_1G_disk1 aun=0 blkn=0  | egrep 'type'
kfbh.type:                            1 ; 0x002: KFBTYP_DISKHEAD
kfbh.type:                            2 ; 0x002: KFBTYP_FREESPC
kfbh.type:                            3 ; 0x002: KFBTYP_ALLOCTBL
kfbh.type:                            5 ; 0x002: KFBTYP_LISTHEAD
kfbh.type:                           13 ; 0x002: KFBTYP_PST_NONE
kfbh.type:                           18 ; 0x002: KFBTYP_PST_DTA
kfbh.type:                           19 ; 0x002: KFBTYP_HBEAT

Repair ASM disk header block in AU[0] with kfed repair

In ASM versions 11.1.0.7 and later, the ASM disk header block is backed up in the second last ASM metadata block in the allocation unit 1.
Verify ASM DISK Header block located in AU[0] and AU[1]
AU[0] :

[root@grac41 Desktop]# kfed read  /dev/asm_test_1G_disk1 aun=0 blkn=0 | egrep 'name|size|type'
kfbh.type:                            1 ; 0x002: KFBTYP_DISKHEAD
kfdhdb.dskname:               TEST_0000 ; 0x028: length=9
kfdhdb.grpname:                    TEST ; 0x048: length=4
kfdhdb.fgname:                TEST_0000 ; 0x068: length=9
kfdhdb.capname:                         ; 0x088: length=0
kfdhdb.secsize:                     512 ; 0x0b8: 0x0200
kfdhdb.blksize:                    4096 ; 0x0ba: 0x1000
kfdhdb.ausize:                  1048576 ; 0x0bc: 0x00100000
kfdhdb.dsksize:                    1023 ; 0x0c4: 0x000003ff

AU[1] :

[root@grac41 Desktop]# kfed read  /dev/asm_test_1G_disk1 aun=1 blkn=254  | egrep 'name|size|type'
kfbh.type:                            1 ; 0x002: KFBTYP_DISKHEAD
kfdhdb.dskname:               TEST_0000 ; 0x028: length=9
kfdhdb.grpname:                    TEST ; 0x048: length=4
kfdhdb.fgname:                TEST_0000 ; 0x068: length=9
kfdhdb.capname:                         ; 0x088: length=0
kfdhdb.secsize:                     512 ; 0x0b8: 0x0200
kfdhdb.blksize:                    4096 ; 0x0ba: 0x1000
kfdhdb.ausize:                  1048576 ; 0x0bc: 0x00100000
kfdhdb.dsksize:                    1023 ; 0x0c4: 0x000003ff

Erase Disk header block in first AU ( aun=0 blkn=0 )

# dd if=/dev/zero of=/dev/asm_test_1G_disk1  bs=4096 count=1

Verify ASM disk header

# kfed read /dev/asm_test_1G_disk1 aun=0 blkn=0
kfbh.type:                            0 ; 0x002: KFBTYP_INVALID
KFED-00322: Invalid content encountered during block traversal: [kfbtTraverseBlock][Invalid OSM block type][][0]
--> Corrupted ASM disk header detected in AU [0]

Repair disk header in AU[0] with kfed

[grid@grac41 ASM]$ kfed repair  /dev/asm_test_1G_disk1
[grid@grac41 ASM]$ kfed read /dev/asm_test_1G_disk1 aun=0 blkn=0
kfbh.type:                            1 ; 0x002: KFBTYP_DISKHEAD
kfdhdb.dskname:               TEST_0000 ; 0x028: length=9
kfdhdb.grpname:                    TEST ; 0x048: length=4
kfdhdb.fgname:                TEST_0000 ; 0x068: length=9
kfdhdb.capname:                         ; 0x088: length=0
kfdhdb.secsize:                     512 ; 0x0b8: 0x0200
kfdhdb.blksize:                    4096 ; 0x0ba: 0x1000
kfdhdb.ausize:                  1048576 ; 0x0bc: 0x00100000
kfdhdb.dsksize:                    1023 ; 0x0c4: 0x000003ff
--> kfed repair worked - Disk header restored

Can kfed repair the Disk header block stored in the 2.nd AU ?

Delete Disk header block in AU[1]
First use dd to figure out whether we are getting the correct block

[grid@grac41 ASM]$  dd if=/dev/asm_test_1G_disk1 of=-  bs=4096 count=1 skip=510 ; strings block1
1+0 records in
1+0 records out
4096 bytes (4.1 kB) copied, 0.000464628 s, 8.8 MB/s
ORCLDISK
TEST_0000
TEST
TEST_0000
--> looks like an ASM disk header - go ahead and erase that block

[grid@grac41 ASM]$  dd if=/dev/zero of=/dev/asm_test_1G_disk1  bs=4096 count=1  seek=510
1+0 records in
1+0 records out
4096 bytes (4.1 kB) copied, 0.00644028 s, 636 kB/s

Verify ASM disk header block in AU[1]

[grid@grac41 ASM]$ kfed read /dev/asm_test_1G_disk1 aun=1 blkn=254
kfbh.type:                            0 ; 0x002: KFBTYP_INVALID
KFED-00322: Invalid content encountered during block traversal: [kfbtTraverseBlock][Invalid OSM block type][][0]
--> Corrupted ASM disk header detected

[grid@grac41 ASM]$ kfed repair  /dev/asm_test_1G_disk1
KFED-00320: Invalid block num1 = [0], num2 = [1], error = [endian_kfbh]
--> kfed repair doesn' work

Repair block with dd

grid@grac41 ASM]$ dd if=/dev/asm_test_1G_disk1  bs=4096  count=1 of=/dev/asm_test_1G_disk1  bs=4096 count=1  seek=510
1+0 records in
1+0 records out
4096 bytes (4.1 kB) copied, 0.0306682 s, 134 kB/s
[grid@grac41 ASM]$ kfed read /dev/asm_test_1G_disk1 aun=0 blkn=0
kfbh.type:                            1 ; 0x002: KFBTYP_DISKHEAD
kfdhdb.dskname:               TEST_0000 ; 0x028: length=9
kfdhdb.grpname:                    TEST ; 0x048: length=4
kfdhdb.fgname:                TEST_0000 ; 0x068: length=9
kfdhdb.capname:                         ; 0x088: length=0
kfdhdb.secsize:                     512 ; 0x0b8: 0x0200
kfdhdb.blksize:                    4096 ; 0x0ba: 0x1000
kfdhdb.ausize:                  1048576 ; 0x0bc: 0x00100000
kfdhdb.dsksize:                    1023 ; 0x0c4: 0x000003ff

# kfed read /dev/asm_test_1G_disk1 aun=1 blkn=254
kfbh.type:                            1 ; 0x002: KFBTYP_DISKHEAD
kfdhdb.dskname:               TEST_0000 ; 0x028: length=9
kfdhdb.grpname:                    TEST ; 0x048: length=4
kfdhdb.fgname:                TEST_0000 ; 0x068: length=9
kfdhdb.capname:                         ; 0x088: length=0
kfdhdb.secsize:                     512 ; 0x0b8: 0x0200
kfdhdb.blksize:                    4096 ; 0x0ba: 0x1000
kfdhdb.ausize:                  1048576 ; 0x0bc: 0x00100000
kfdhdb.dsksize:                    1023 ; 0x0c4: 0x000003ff

Summary:

to fix the backup block or the ASM disk header in AU 1 block you need to use dd

Reference:

http://laurent-leturgez.com/2012/11/12/how-asm-disk-header-block-repair-works/
http://asmsupportguy.blogspot.fr/2010/04/kfed-asm-metadata-editor.html
http://asmsupportguy.blogspot.co.uk/2011/08/asm-disk-header.html