Parameter used in Oracle ASM Configuration

Following are the Oracle ASM parameter used in spfile:

ASM_DISKGROUPS:
List of all diskgroups mounted at time of ASM instance startup.
Oracle ASM automatically adds and remove the disk group to the parameter when the disk group is successfully created or mounted or removed.
Startup mount command will fire the ALTER DISKGROUP ALL MOUNT command which mount all diskgroup listed in this parameter.
Example:

--entry in pfile or spfile
ASM_DISKGROUPS = DATA

-- You can manually change the value as
ALTER SYSTEM SET ASM_DISKGROUPS = DATA, FRA;

Note: Oracle 12c release 1 or later support 511 diskgroups before it only support 63 diskgroups

ASM_DISKSTRING:
It specifies a comma-delimited list of strings that limits the set of disks that an ASM instance discovers.
Example:

--all
ASM_DISKSTRING = /dev/rdsk/mydisks/*
-- limit
ASM_DISKSTRING = '/dev/rdsk/*disk3', '/dev/rdsk/*disk4'


ASM_IO_PROCESSES:
It specifies the number of IO worker processes to be started in an Oracle IOServer (IOS) server instance.
Parameter is only applicable for an Oracle IOServer instance, which runs in an Oracle Grid Infrastructure home.

ASM_POWER_LIMIT:
It specifies the default power for disk rebalancing in a disk group. It is used to rebalancing operation across disks when in added and removed from diskgroup.
Range of values is 0 to 1024. The default value is 1. A value of 0 disables rebalancing.

the power of the rebalancing operation in a disk group with the
POWER clause of the SQL ALTER DISKGROUP .. REBALANCE statement


ASM_PREFERRED_READ_FAILURE_GROUPS:
It is depreciated in 12.2 Oracle version. It is used to specifies the failure groups