Disk Size Variance (%) lists the percentage difference in size between the largest and smallest disks in the disk group. This will be zero if best practices have been followed and all disks are the same size.
Small differences in size are acceptable. Large differences can result in some disks getting much more I/O than others. With normal or high redundancy disk groups, a large size variance can make it impossible to reduce the percent imbalance to a small value.
The rest of the information in this section is only valid for this metric when it appears in either the Enterprise Manager Grid Control or the Enterprise Manager Database Control (if applicable).
The following table shows how often the metric's value is collected.
|
Target Version |
Collection Frequency |
|
10.1.0.x; 10.2.0.x; 11.1.0.x; 11.2.0.x |
Every 15 Minutes |
Disk Size Variance (%) is calculated as 100 * (max(total_mb) - min(total_mb)) / max(total_mb), where total_mb is a column in V$ASM_DISK_STAT.
A large size variance may require a configuration change to provide an even distribution of file extents and space usage across all disks in a disk group.
Related Topics
About Alerts
About the Metric Detail Page
Editing Thresholds
Understanding Line Charts
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