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