Oracle ASM : Monitor Disk Group Space Usage in 19c

In Oracle 19c environments using ASM (Automatic Storage Management), monitoring disk group space is critical for ensuring database stability and avoiding storage-related outages.

The following query provides a quick and clear view of ASM disk group utilization, including:

• Total space
• Free space
• Used space
• Percentage utilization

Purpose of the Query

This query helps DBAs to:

• Monitor ASM storage consumption
• Identify disk groups running low on space
• Plan disk additions or rebalance operations
• Prevent ORA-15041 / ORA-15042 space issues

SELECT name as "ASM Group",
       round((total_mb-free_mb)/1024) as "USED Size (Gb)",
       round(free_mb/1024) "Free Size (Gb)",
       round(total_mb/1024) "Total Size(Gb)",
       round((total_mb-free_mb)/total_mb*100) as "USED Size (%)"
FROM v$asm_diskgroup
ORDER BY round((total_mb-free_mb)/total_mb*100) DESC;

How It Works

1. ASM Disk Groups Source

The view V$ASM_DISKGROUP provides real-time metadata about ASM storage groups, including:

• TOTAL_MB → total allocated space
• FREE_MB → available free space

Each row represents one ASM disk group such as:

• DATA
• RECO
• FRA

Interpretation

High utilization (>80%)

• Risk of space exhaustion
• Potential ASM rebalance activity required
• Immediate monitoring needed

Medium utilization (50–80%)

• Normal production usage
• Should be monitored regularly

Low utilization (<50%)

• Healthy free space
• Good for future growth or backups (FRA)

Practical Use Cases

This query is essential for:

• ASM capacity monitoring
• Storage planning
• Cloud or SAN resource optimization
• Preventing database downtime due to disk full issues
• RAC and Data Guard environments