Oracle ASM Interview Questions/FAQs

1. What is the use of ASM (or) Why ASM preferred over filesystem?
ASM provides striping and mirroring.

2. What are the init parameters related to ASM?
INSTANCE_TYPE = ASM
ASM_POWER_LIMIT = 11
ASM_DISKSTRING = '/dev/rdsk/*s2', '/dev/rdsk/c1*'
ASM_DISKGROUPS = DG_DATA, DG_FRA

3. What is rebalancing (or) what is the use of ASM_POWER_LIMIT?
ASM_POWER_LIMIT is dynamic parameter, which will be useful for rebalancing the data across disks.
Value can be 1(lowest) to 11 (highest).

4. What are different types of redundancies in ASM & explain?
External redundancy,
Normal redundancy,
High redundancy.

5. How to copy file to/from ASM from/to filesystem?
By using ASMCMD cp command

6. How to find out the databases, which are using the ASM instance?
ASMCMD> lsct
SQL> select DB_NAME from V$ASM_CLIENT;

7. What are different types of stripings in ASM & their differences?
Fine-grained striping
Coarse-grained striping
lsdg
select NAME,ALLOCATION_UNIT_SIZE from v$asm_diskgroup;

8. What is allocation unit and what is default value of au_size and how to change?
Every ASM disk is divided into allocation units (AU). An AU is the fundamental unit of allocation within a disk group. A file extent consists of one or more AU. An ASM file consists of one or more file extents.
CREATE DISKGROUP disk_group_2 EXTERNAL REDUNDANCY DISK '/dev/sde1' ATRRIBUTE 'au_size' = '32M';

9. What are the background processes in ASM?

10. What process does the rebalancing?
RBAL, ARBn

11. How to add/remove disk to/from diskgroup?