DBA manage databases on ASM & manages ASM disk groups. When we notice the disk group holding database is filled, DBA will add Brand new disk to existing disk group. Here I want to elaborate the background process of ASM i.e (ARBx), How ASM will perform rebalancing operation? ASM allocate ARBx( Actual Rebalancing process ) to perform rebalancing operation inside the disk group. ARBx is responsible for data movement between disks inside the disk group. The number of rebalancing process allocated depend on ASM_POWER_LIMIT value. Based on ASM disk group compatibility, we can alter ASM_POWER_LIMIT
if disk group asm compatibility >= 11.2.0.2 ( alter asm_power_limit from 0 to 1024)
if disk group asm compatibility < 11.2.0.2 ( alter asm_power_limit from 0 to 11)
Query to check ASM disk group compatibility using v$asm_diskgroup
col COMPATIBILITY form a10
SQL> col DATABASE_COMPATIBILITY form a10
SQL> col NAME form a20
SQL> select group_number, name,
compatibility, database_compatibility from v$asm_diskgroup;
col COMPATIBILITY form a10
SQL> col DATABASE_COMPATIBILITY form a10
SQL> col NAME form a20
SQL> select group_number, name,
compatibility, database_compatibility from v$asm_diskgroup;
Regularly when we will add disk to the disk group by logging into SYSASM (or) using ASMCA
sql> conn / as sysasm
sql> alter diskgroup stage add disk '/dev/asm-disk8','/dev/asm-disk9';
sql>alter diskgroup DISKGROUP rebalance power 5;
when you say 5, 5 actual rebalancing (ARBx) process are allocated inside the diskgroup to improve performance we can alter this number to higher value, where 0 will disable the Rebalancing process
Query performance of ASM_ Rebalancing operation can be monitored using "v$asm_operation"
SQL> select group_number,operation,state,power,est_minutes from v$asm_operation;
Note > It is always recommended to add a disk to existing disk group during off hours, rebalancing operation will impact the performance of database
Related Links to ASM #
Adding disk to existing diskgroup
http://www.oracleinmemory.com/search?q=adding+disk+to+diskgroup
ACFS RAC ASM
http://www.oracleinmemory.com/2016/03/acfs-automatic-cluster-filesystem-on.html
ASMCMD> ASM command line utility
http://www.oracleinmemory.com/2016/01/asm-asmcmd.html
Adding disk to existing diskgroup
http://www.oracleinmemory.com/search?q=adding+disk+to+diskgroup
ACFS RAC ASM
http://www.oracleinmemory.com/2016/03/acfs-automatic-cluster-filesystem-on.html
ASMCMD> ASM command line utility
http://www.oracleinmemory.com/2016/01/asm-asmcmd.html
Adding a disk to diskgroup > ASM
