Disk I/O Saturation

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Resource ContentionUpdated Feb 6, 2026

High disk I/O wait times slow query execution and merge operations, often caused by undersized storage, sequential I/O patterns, or competing workloads.

Sources

Common issues you can solve using advanced monitoring ...clickhouse.com

How to Monitor ClickHouse Query Performance with OpenTelemetryoneuptime.com

Technologies:

ClickHouseSymptoms of this issue are visible in ClickHouse metrics and logs

clickhouse.metric.IOWait

How to detect:

Monitor IOWait from system metrics and ReadFromDisk/WriteBufferFromFileDescriptorWriteBytes from ProfileEvents. Alert when IOWait consistently exceeds 20% or disk read/write rates approach hardware limits.

Recommended action:

Upgrade to faster storage (NVMe SSDs), implement tiered storage with hot/cold data separation, optimize table codecs for better compression (reduce I/O), or distribute data across more nodes to parallelize I/O.