10 Oracle ASM Interview Questions and Answers

Oracle Automatic Storage Management (ASM) is a critical component for managing database storage in Oracle environments. It simplifies the storage and management of Oracle database files, providing a high-performance, scalable, and reliable solution. ASM automates the striping and mirroring of database files, which enhances performance and ensures data redundancy without the need for third-party software.

This article offers a curated selection of interview questions designed to test your knowledge and understanding of Oracle ASM. By reviewing these questions and their detailed answers, you will be better prepared to demonstrate your expertise and problem-solving abilities in Oracle ASM during your interview.

Oracle ASM Interview Questions and Answers

1. Describe how ASM disk groups are created and managed.

Oracle ASM (Automatic Storage Management) is a feature of Oracle Database that simplifies storage management by allowing administrators to manage disk groups rather than individual disks.

To create and manage ASM disk groups, the following steps are typically involved:

• Disk Discovery: ASM discovers disks available for use using the ASM_DISKSTRING initialization parameter, which specifies the search path for ASM disks.
• Creating Disk Groups: Disk groups are created using the CREATE DISKGROUP SQL statement, specifying the name, redundancy level, and list of disks.
• Managing Disk Groups: Disk groups can be managed using SQL statements and ASM commands, such as ALTER DISKGROUP to add or remove disks.
• Monitoring Disk Groups: ASM provides views and tools for monitoring disk group status and performance, like the V$ASM_DISKGROUP view and asmcmd tool.

Example of creating a disk group:

CREATE DISKGROUP data NORMAL REDUNDANCY
  DISK '/dev/sda1', '/dev/sdb1';

2. Explain the concept of ASM redundancy levels and their impact on storage.

Oracle ASM provides three redundancy levels: External, Normal, and High. These levels determine data mirroring and protection against disk failures.

External Redundancy: ASM does not provide mirroring, relying on the underlying storage system for redundancy.

Normal Redundancy: Provides two-way mirroring, storing each piece of data twice on different disks, protecting against single disk failure.

High Redundancy: Offers three-way mirroring, storing data three times on different disks, protecting against two simultaneous disk failures.

The chosen redundancy level impacts storage usage: External uses the least, Normal uses approximately twice the storage, and High uses about three times the storage space.

3. How would you migrate a database from non-ASM to ASM storage?

Migrating a database from non-ASM to ASM storage involves several steps:

1. Prepare the ASM Environment: Ensure the ASM instance is configured and running, and create necessary ASM disk groups.
2. Backup the Database: Perform a full backup to ensure data safety during migration.
3. Convert the Database Files: Use RMAN to convert files from non-ASM to ASM storage, updating control files accordingly.
4. Update the Database Configuration: Modify initialization parameters to reflect new ASM storage locations.
5. Test the Migration: Bring the database online and test to ensure successful migration.
6. Monitor and Optimize: Monitor performance and adjust to optimize ASM storage use.

4. Describe the role of ASM instance parameters and how they affect performance.

ASM instance parameters influence storage resource management and performance. Key parameters include:

• ASM_DISKSTRING: Specifies search paths for discovering ASM disks, ensuring efficient disk utilization.
• ASM_POWER_LIMIT: Controls rebalance operation speed, balancing resource use and operation speed.
• ASM_PREFERRED_READ_FAILURE_GROUPS: Defines preferred read failure groups to optimize read performance.
• ASM_DISKGROUPS: Lists disk groups the ASM instance should mount at startup, affecting performance.
• ASM_IO_PROCESSES: Specifies the number of I/O worker processes, improving I/O throughput in high-demand environments.

5. How does ASM handle file striping and mirroring?

ASM handles file striping and mirroring to optimize performance and ensure data redundancy.

File striping distributes data across multiple disks to balance the I/O load. ASM automatically stripes files into allocation units (AUs) and spreads them across available disks, improving read and write performance.

Mirroring provides data redundancy, with ASM supporting two-way and three-way mirroring. Two-way mirroring maintains two copies of each AU on different disks, while three-way mirroring maintains three copies. This redundancy protects data against disk failures, allowing ASM to reconstruct lost data from mirrored copies.

ASM offers flexibility in managing redundancy through disk groups, configurable with different redundancy levels: external (no mirroring), normal (two-way mirroring), and high (three-way mirroring).

6. Explain the process of adding and removing disks from an ASM disk group.

Adding and removing disks from an ASM disk group involves specific SQL commands.

To add a disk, use the ALTER DISKGROUP command:

ALTER DISKGROUP disk_group_name ADD DISK 'disk_path';

To remove a disk, use:

ALTER DISKGROUP disk_group_name DROP DISK 'disk_name';

Monitor the rebalance operation using the V$ASM_OPERATION view:

SELECT * FROM V$ASM_OPERATION;

7. Discuss the impact of ASM on database performance and how to optimize it.

ASM impacts database performance by simplifying storage management and providing high-performance, scalable, and reliable storage solutions. Key features include:

• Striping: Balances I/O load by striping data across all available disks.
• Mirroring: Enhances data availability and reliability through redundancy.
• Automatic Rebalancing: Ensures optimal performance by automatically rebalancing data across disks.
• Reduced Management Overhead: Simplifies storage management, allowing DBAs to focus on performance tuning.

To optimize ASM performance, consider these best practices:

• Disk Group Configuration: Use an appropriate number of disks to ensure balanced I/O distribution.
• ASM Disk Attributes: Configure attributes like AU_SIZE and DISK_REPAIR_TIME to match workload requirements.
• Monitoring and Tuning: Regularly monitor ASM performance and address I/O bottlenecks or imbalances.
• ASM Instance Configuration: Ensure sufficient memory and CPU resources, and configure parameters like ASM_POWER_LIMIT.
• Use of Oracle Exadata: Consider using Oracle Exadata for high-performance environments.

8. How do you configure ASM for high availability?

To configure ASM for high availability, consider these components and practices:

• Redundancy Levels: Choose appropriate redundancy levels for data availability.
• Disk Groups: Create multiple disk groups to distribute I/O load and provide fault tolerance.
• Cluster Configuration: Use Oracle Clusterware for failover capabilities in a clustered environment.
• ASM Instance Monitoring: Regularly monitor ASM instances to ensure they are running and healthy.
• Backup and Recovery: Implement a robust backup and recovery strategy using RMAN.
• Network Configuration: Optimize network configuration for high availability with redundant interfaces.

9. What are the best practices for configuring ASM for optimal performance?

For optimal ASM performance, follow these best practices:

• Disk Group Configuration: Use multiple disk groups to separate workloads and avoid contention.
• Redundancy: Choose the appropriate redundancy level based on requirements.
• Striping: Ensure disks have similar performance characteristics to avoid bottlenecks.
• Allocation Unit Size: Consider increasing AU size for large databases to improve performance.
• Disk I/O Balance: Monitor and balance I/O across disks to prevent bottlenecks.
• ASM Instance Parameters: Tune parameters like ASM_POWER_LIMIT and ASM_DISKSTRING.
• Regular Maintenance: Perform regular maintenance tasks like checking disk group integrity.

10. Explain the process of upgrading ASM and any considerations that need to be taken into account.

Upgrading ASM involves several steps and considerations:

• Pre-Upgrade Checks: Assess the current ASM environment for compatibility and requirements.
• Backup: Take a full backup of ASM metadata and database files.
• Upgrade Grid Infrastructure: Upgrade Oracle Grid Infrastructure using OUI or command-line interface.
• Post-Upgrade Tasks: Verify ASM configuration and ensure database instances connect to upgraded ASM.
• Testing: Conduct thorough testing to ensure the upgraded environment functions correctly.

Considerations include:

• Scheduling the upgrade during a maintenance window to minimize downtime.
• Communicating the upgrade plan and potential impact to stakeholders.
• Verifying compatibility of third-party tools and applications with the new version.
• Monitoring the system closely during and after the upgrade to identify and resolve issues.