Allocation units per ASM file

Check AUSIZE and diskgroup redundancy

SQL> select NAME, GROUP_NUMBER, ALLOCATION_UNIT_SIZE/1024/1024 “AU size (MB)”, TYPE
from V$ASM_DISKGROUP
where NAME=’DATA’; 2 3

NAME GROUP_NUMBER AU size (MB) TYPE
—————————— ———— ———— ——
DATA 2 1 EXTERN
Create two tablespaces small (<60 extents) and large(> 60 extents)

SQL> create tablespace T1 datafile ‘+DATA’ size 10M;

Tablespace created.

SQL> create tablespace T2 datafile ‘+DATA’ size 100 M;

Tablespace created.
SQL> select name,round(bytes/1024/1024) from v$datafile;

NAME
——————————————————————————–
ROUND(BYTES/1024/1024)
———————-
+DATA/test/datafile/t1.522.869781375
10

+DATA/test/datafile/t2.523.869781387
100

SQL> select FILE_NUMBER, round(BYTES/1024/1024) “Bytes (AU)”, round(SPACE/1024/1024) “Space (AUs)”, REDUNDANCY from V$ASM_FILE where FILE_NUMBER in (522,523)and GROUP_NUMBER=2;

FILE_NUMBER Bytes (AU) Space (AUs) REDUND
———– ———- ———– ——
522 10 11 UNPROT
523 100 102 UNPROT
SQL> select XNUM_KFFXP “Virtual extent”, PXN_KFFXP “Physical extent”, DISK_KFFXP “Disk number”, AU_KFFXP “AU number”
from X$KFFXP
where GROUP_KFFXP=2 and NUMBER_KFFXP=523 2 3 ;

Virtual extent Physical extent Disk number AU number
————– ————— ———– ———-
0 0 0 1374
1 1 1 1354
2 2 0 1375
3 3 1 1355
4 4 0 1376
5 5 1 1356
6 6 0 1377
.
.
.
95 95 1 1402
96 96 0 1422
97 97 1 1403
98 98 0 1423

Virtual extent Physical extent Disk number AU number
————– ————— ———– ———-
99 99 1 1404
100 100 0 1424
2147483648 0 1 1384

102 rows selected.
SQL> select DISK_NUMBER, PATH
from V$ASM_DISK
where GROUP_NUMBER=2; 2 3

DISK_NUMBER
———–
PATH
——————————————————————————–
0
ORCL:ASMDISK1

1
ORCL:ASMDISK2

racle@VM2 ~]$ kfed read aun=1384 dev=/dev/oracleasm/disks/ASMDISK2| grep type
kfbh.type: 12 ; 0x002: KFBTYP_INDIRECT
These additional allocation units hold ASM metadata for the large file. More specifically they hold extent map information that could not fit into the the ASM file directory block. The file directory needs extra space to keep track of files larger than 60 extents, so it needs an additional allocation unit to do so. While the file directory needs only few extra ASM metadata blocks, the smallest unit of space the ASM can allocate is an AU. And because this is metadata, this AU is triple mirrored (even in a normal redundancy disk group), hence 3 extra allocation units for the large file. In an external redundancy disk group, there would be only one extra AU per large file.

Ref:

http://asmsupportguy.blogspot.fr/search?updated-max=2013-08-14T20:41:00%2B10:00&max-results=2&start=13&by-date=false

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