Oracle ASM的AU（Allocation units）分配

Oracle ASM的AU（Allocation units）分配

作者：eygle |
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ASM在分配空间时，以AU为单位进行，AU即Allocation units，是组成ASM disk的基本单元。

在Oracle 10gR2中，ASM AU的缺省单位大小是1M，相应的条带大小是128K。

在ASM中，可以通过调整_asm_ausize隐含参数的大小来进行调整，_asm_stripesize控制相应的条带化参数。

从v$asm_diskgroup视图可以查询得到相关的信息：

SQL> select group_number,name,sector_size,block_size,allocation_unit_size from v$asm_diskgroup;

GROUP_NUMBER NAME SECTOR_SIZE BLOCK_SIZE ALLOCATION_UNIT_SIZE

------------ ------ ----------- ---------- --------------------

1 ARCHDG 512 4096 1048576

2 DATADG 512 4096 1048576

在Oracle Database 11g中，可以通过类似如下语句在创建磁盘组时指定au_size:

SQL> CREATE DISKGROUP DATA DISK '/dev/raw/raw15', '/dev/raw/raw16',

'/dev/raw/raw17' ATTRIBUTE 'au_size' = '16M', 'compatible.asm' = '11.1' 'compatible.rdbms' = '11.1';

ASM允许的相关参数可以从DB的实例中查询获得，以下是一系列和asm相关的初始化参数：

SQL> SELECT x.ksppinm NAME, y.ksppstvl VALUE, x.ksppdesc describ

2 FROM SYS.x$ksppi x, SYS.x$ksppcv y

3 WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%';

Enter value for par: asm

old 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'

new 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%asm%'

NAME VALUE DESCRIB

------------------------------ -------------------- ------------------------------------------------------------

asm_diskstring disk set locations for discovery

_asm_disk_repair_time 14400 seconds to wait before dropping a failing disk

asm_diskgroups disk groups to mount automatically

asm_power_limit 1 number of processes for disk rebalancing

_asm_ausize 1048576 allocation unit size

_asm_blksize 4096 metadata block size

_asm_acd_chunks 1 initial ACD chunks created

_asm_libraries ufs library search order for discovery

_asm_maxio 1048576 Maximum size of individual I/O request

_asm_allow_only_raw_disks TRUE Discovery only raw devices

_asmlib_test 0 Osmlib test event

NAME VALUE DESCRIB

------------------------------ -------------------- ------------------------------------------------------------

_asm_allow_resilver_corruption FALSE Enable disk resilvering for external redundancy

_asmsid asm ASM instance id

_asm_wait_time 18 Max/imum time to wait before asmb exits

_asm_stripewidth 8 ASM file stripe width

_asm_stripesize 131072 ASM file stripe size

_asm_droptimeout 60 timeout before offlined disks get dropped (in 3s ticks)

_asm_emulmax 10000 max number of concurrent disks to emulate I/O errors

_asm_emultimeout 0 timeout before emulation begins (in 3s ticks)

_asm_kfdpevent 0 KFDP event

20 rows selected.