尽管Oracle缺省都是使用裸设备来创建ASM磁盘，但其实Oracle也允许使用普通文件来创建ASM磁盘，
当然这种方法最好只用在测试环境下或者学习环境下，不能用在生产环境下。之所以必须要用裸设备，
是因为有一个隐含参数_asm_allow_only_raw_disks在起作用。
通过SQL查看ASM参数：
set lines
col name for a30
col value for a10
col DESCRIPTION for a50 SQL> select x.ksppinm name,y.ksppstvl value,x.ksppdesc description
from x$ksppi x,x$ksppcv y
where x.inst_id=userenv('Instance')
and y.inst_id=userenv('Instance')
and x.indx=y.indx
and x.ksppinm like '_asm_allow_only_raw_disks%'
order by name; NAME VALUE DESCRIPTION
------------------------------ ---------- --------------------------------------------------
_asm_allow_only_raw_disks TRUE Discovery only raw devices
只要把这个参数改成FALSE，我们就可以使用文件来创建ASM了。试验如下：
1.使用dd命令创建几个文件
[oracle@std u02]$ mkdir asmfile
[oracle@std u02]$ cd asmfile/
[oracle@std asmfile]$ dd if=/dev/zero of=cp1 bs=1M count=
+ records in
+ records out
bytes ( MB) copied, 5.50622 seconds, 95.2 MB/s
[oracle@std asmfile]$ dd if=/dev/zero of=cp2 bs=1M count=
+ records in
+ records out
bytes ( MB) copied, 7.13052 seconds, 73.5 MB/s
[oracle@std asmfile]$ dd if=/dev/zero of=cp3 bs=1M count=
+ records in
+ records out
bytes ( MB) copied, 6.60984 seconds, 79.3 MB/s
[oracle@std asmfile]$ dd if=/dev/zero of=cp4 bs=1M count=
+ records in
+ records out
bytes ( MB) copied, 5.31099 seconds, 98.7 MB/s
[oracle@std asmfile]$ ls -l
total
-rw-r--r-- oracle oinstall Feb : cp1
-rw-r--r-- oracle oinstall Feb : cp2
-rw-r--r-- oracle oinstall Feb : cp3
-rw-r--r-- oracle oinstall Feb : cp4
2.创建asm参数文件并修改asm_diskstring
--注意asm_diskstrint参数设置
[oracle@std dbs]$ cp init+ASM.ora init+ASM2.ora
[oracle@std dbs]$ vi init+ASM2.ora
[oracle@std dbs]$ cat init+ASM2.ora
*.asm_diskstring='/u02/asmfile/cp*'
*.instance_type='asm'
*.large_pool_size=24M
*.remote_login_passwordfile='SHARED'
*.background_dump_dest='/u02/app/admin/+ASM2/bdump'
*.core_dump_dest='/u02/app/admin/+ASM2/cdump'
*.user_dump_dest='/u02/app/admin/+ASM2/bdump'
3.启动ASM实例
[oracle@std dbs]$ export ORACLE_SID=+ASM2
[oracle@std dbs]$ sqlplus '/as sysdba' SQL*Plus: Release 10.2.0.4. - Production on Mon Feb :: Copyright (c) , , Oracle. All Rights Reserved. Connected to an idle instance. SQL> startup
ASM instance started Total System Global Area bytes
Fixed Size bytes
Variable Size bytes
ASM Cache bytes
ORA-: no diskgroups mounted SQL> select path from v$asm_disk; no rows selected
启动ASM实例后还看不到我们asm_diskstring参数指定的设置!!!
4.修改隐含参数，重启ASM实例
[oracle@std dbs]$ vi init+ASM2.ora
[oracle@std dbs]$ cat init+ASM2.ora
*.asm_diskstring='/u02/asmfile/cp*'
*.instance_type='asm'
*.large_pool_size=24M
*.remote_login_passwordfile='SHARED'
*.background_dump_dest='/u02/app/admin/+ASM2/bdump'
*.core_dump_dest='/u02/app/admin/+ASM2/cdump'
*.user_dump_dest='/u02/app/admin/+ASM2/bdump'
_asm_allow_only_raw_disks= FALSE
[oracle@std dbs]$ export ORACLE_SID=+ASM2
[oracle@std dbs]$ sqlplus '/as sysdba' SQL*Plus: Release 10.2.0.4. - Production on Mon Feb :: Copyright (c) , , Oracle. All Rights Reserved. Connected to an idle instance. SQL> startup
ASM instance started Total System Global Area bytes
Fixed Size bytes
Variable Size bytes
ASM Cache bytes
ORA-: no diskgroups mounted SQL> select path from v$asm_disk; PATH
--------------------------------------------------------------------------------
/u02/asmfile/cp4
/u02/asmfile/cp1
/u02/asmfile/cp2
/u02/asmfile/cp3
现在可以看到修改参数后可以看到asm_diskstring参数指定的磁盘了，现在看一下是否能够创建磁盘组
5.创建磁盘组
--注意这些创建的磁盘组不会写入init+ASM2.ora，因为我们当前使用的是pfile,重启实例会丢失。
SQL> create diskgroup dg normal redundancy disk
'/u02/asmfile/cp1','/u02/asmfile/cp2' name dg_data; Diskgroup created. SQL> create diskgroup back normal redundancy
disk '/u02/asmfile/cp3','/u02/asmfile/cp4' name backup_data; Diskgroup created.
--每个磁盘都分配了名字
SQL> select name,path from v$asm_disk; NAME PATH
-------------------- --------------------------------------------------
BACKUP_DATA /u02/asmfile/cp4
BACK_0000 /u02/asmfile/cp3
DG_DATA /u02/asmfile/cp2
DG_0000 /u02/asmfile/cp1
6.查看磁盘组的属性
SQL> select name,block_size,allocation_unit_size from v$asm_diskgroup; NAME BLOCK_SIZE ALLOCATION_UNIT_SIZE
-------------------- ---------- --------------------
DG
BACK
上面的SQL查询了磁盘组的数据块大小及分配单元，其实这两个属性也是由隐含参数控制的，
--查询ASM的隐含参数，这些参数没有十足的把握尽量不要修改
SQL> set lines
SQL> col name for a30
SQL> col value for a10
SQL> col DESCRIPTION for a50
SQL> select x.ksppinm name,y.ksppstvl value,x.ksppdesc description
from x$ksppi x,x$ksppcv y
where x.inst_id=userenv('Instance')
and y.inst_id=userenv('Instance')
and x.indx=y.indx
and x.ksppinm like '_asm%'
order by name; NAME VALUE DESCRIPTION
------------------------------ ---------- --------------------------------------------------
_asm_acd_chunks initial ACD chunks created
_asm_allow_only_raw_disks FALSE Discovery only raw devices
_asm_allow_resilver_corruption FALSE Enable disk resilvering for external redundancy
_asm_ausize allocation unit size --指定了分配单元
_asm_blksize metadata block size --指定了数据块大小
_asm_disk_repair_time seconds to wait before dropping a failing disk
_asm_droptimeout timeout before offlined disks get dropped (in 3s t
icks) _asm_emulmax max number of concurrent disks to emulate I/O erro
rs NAME VALUE DESCRIPTION
------------------------------ ---------- -------------------------------------------------- _asm_emultimeout timeout before emulation begins (in 3s ticks)
_asm_kfdpevent KFDP event
_asm_libraries ufs library search order for discovery
_asm_maxio Maximum size of individual I/O request
_asm_skip_resize_check FALSE skip the checking of the clients for s/w compatibi
lity for resize _asm_stripesize ASM file stripe size
_asm_stripewidth ASM file stripe width
_asm_wait_time Max/imum time to wait before asmb exits NAME VALUE DESCRIPTION
------------------------------ ---------- --------------------------------------------------
_asmlib_test Osmlib test event
_asmsid asm ASM instance id rows selected. SQL>
致谢：本文章参考了张晓明<<大话Oracle RAC 集群 高可用性 备份与恢复>>