Disk I/O Bottleneck During Merge

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Resource ContentionUpdated Feb 6, 2026

Segment merges saturate disk I/O causing Disk_Utilization spikes and elevated Disk_WaitTime, leading to query slowdowns and potential timeout failures. Merge_Time and Indexing_ThrottleTime increase as OpenSearch throttles indexing to protect disk resources.

Sources

Metrics referencedocs.opensearch.org

Technologies:

OpenSearchSymptoms of this issue are visible in OpenSearch metrics and logs

How to detect:

Monitor Disk_Utilization approaching 100% correlated with high Merge_Time, increased Indexing_ThrottleTime, and elevated Disk_WaitTime. Check Merge_CurrentEvent for active merge operations and Disk_ServiceRate for throughput degradation.

Recommended action:

Tune merge policy settings to reduce concurrent merges, upgrade to faster storage (NVMe SSD), reduce indexing rate during peak query times, or scale storage tier horizontally. Monitor IO_TotThroughput to validate improvements.