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 120 col name for a30 col value for a10 col DESCRIPTION for a50 SQL> select x.ksppinm name,y.ksppstvl value,x.ksppdesc description 2 from x$ksppi x,x$ksppcv y 3 where x.inst_id=userenv('Instance') 4 and y.inst_id=userenv('Instance') 5 and x.indx=y.indx 6 and x.ksppinm like '_asm_allow_only_raw_disks%' 7 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=500 500+0 records in 500+0 records out 524288000 bytes (524 MB) copied, 5.50622 seconds, 95.2 MB/s [oracle@std asmfile]$ dd if=/dev/zero of=cp2 bs=1M count=500 500+0 records in 500+0 records out 524288000 bytes (524 MB) copied, 7.13052 seconds, 73.5 MB/s [oracle@std asmfile]$ dd if=/dev/zero of=cp3 bs=1M count=500 500+0 records in 500+0 records out 524288000 bytes (524 MB) copied, 6.60984 seconds, 79.3 MB/s [oracle@std asmfile]$ dd if=/dev/zero of=cp4 bs=1M count=500 500+0 records in 500+0 records out 524288000 bytes (524 MB) copied, 5.31099 seconds, 98.7 MB/s [oracle@std asmfile]$ ls -l total 2050016 -rw-r--r-- 1 oracle oinstall 524288000 Feb 2 16:23 cp1 -rw-r--r-- 1 oracle oinstall 524288000 Feb 2 16:24 cp2 -rw-r--r-- 1 oracle oinstall 524288000 Feb 2 16:24 cp3 -rw-r--r-- 1 oracle oinstall 524288000 Feb 2 16:24 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 10.2.0.4.0 - Production on Mon Feb 2 16:32:47 2015 Copyright (c) 1982, 2007, Oracle. All Rights Reserved. Connected to an idle instance. SQL> startup ASM instance started Total System Global Area 96468992 bytes Fixed Size 1265984 bytes Variable Size 70037184 bytes ASM Cache 25165824 bytes ORA-15110: 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 10.2.0.4.0 - Production on Mon Feb 2 16:37:38 2015 Copyright (c) 1982, 2007, Oracle. All Rights Reserved. Connected to an idle instance. SQL> startup ASM instance started Total System Global Area 96468992 bytes Fixed Size 1265984 bytes Variable Size 70037184 bytes ASM Cache 25165824 bytes ORA-15110: no diskgroups mounted SQL> select path from v$asm_disk; PATH -------------------------------------------------------------------------------- /u02/asmfile/cp4 /u02/asmfile/cp1 /u02/asmfile/cp2 /u02/asmfile/cp3
现在可以看到修改参数后可以看到asm_diskstring参数指定的磁盘了，现在看一下是否能够创建磁盘组
5.创建磁盘组
--注意这些创建的磁盘组不会写入init+ASM2.ora，因为我们当前使用的是pfile,重启实例会丢失。
SQL> create diskgroup dg normal redundancy disk 2 '/u02/asmfile/cp1','/u02/asmfile/cp2' name dg_data; Diskgroup created. SQL> create diskgroup back normal redundancy 2 disk '/u02/asmfile/cp3','/u02/asmfile/cp4' name backup_data; Diskgroup created.
--每个磁盘都分配了名字
SQL> select name,path from v$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$asm_diskgroup; NAME BLOCK_SIZE ALLOCATION_UNIT_SIZE -------------------- ---------- -------------------- DG 4096 1048576 BACK 4096 1048576
上面的SQL查询了磁盘组的数据块大小及分配单元，其实这两个属性也是由隐含参数控制的，
--查询ASM的隐含参数，这些参数没有十足的把握尽量不要修改
SQL> set lines 120 SQL> col name for a30 SQL> col value for a10 SQL> col DESCRIPTION for a50 SQL> select x.ksppinm name,y.ksppstvl value,x.ksppdesc description 2 from x$ksppi x,x$ksppcv y 3 where x.inst_id=userenv('Instance') 4 and y.inst_id=userenv('Instance') 5 and x.indx=y.indx 6 and x.ksppinm like '_asm%' 7 order by name; NAME VALUE DESCRIPTION ------------------------------ ---------- -------------------------------------------------- _asm_acd_chunks 1 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 1048576 allocation unit size --指定了分配单元 _asm_blksize 4096 metadata block size --指定了数据块大小 _asm_disk_repair_time 14400 seconds to wait before dropping a failing disk _asm_droptimeout 60 timeout before offlined disks get dropped (in 3s t icks) _asm_emulmax 10000 max number of concurrent disks to emulate I/O erro rs NAME VALUE DESCRIPTION ------------------------------ ---------- -------------------------------------------------- _asm_emultimeout 0 timeout before emulation begins (in 3s ticks) _asm_kfdpevent 0 KFDP event _asm_libraries ufs library search order for discovery _asm_maxio 1048576 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 131072 ASM file stripe size _asm_stripewidth 8 ASM file stripe width _asm_wait_time 18 Max/imum time to wait before asmb exits NAME VALUE DESCRIPTION ------------------------------ ---------- -------------------------------------------------- _asmlib_test 0 Osmlib test event _asmsid asm ASM instance id 18 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>>